I have an audio interface, a UMC404HD, that I use both for my speakers and for my microphone. It's plugged in via USB cable. This used to work under Ubuntu 20.10. However something seems to have gone wrong as I updated to 21.04.
The main problem is that I can't select the interface as microphone input any more. The only available input is from my webcam, where previously it allowed me to select the UMC404HD as microphone as well:

404 not found, as they say.
However the device is plugged-in and somehow working. Pavucontrol does show me the device and its volume levels:

These levels peak as I tap on the microphone. It's actually getting input from it. But it's somehow not allowing it to be chosen as a microphone. Note also that the "Port:" drop-down is missing from the UMC404HD device.
In the Configuration tab of Pavucontrol, the device is configured as output+input:

Do you know why the device is not available as microphone input?
EDIT: As requested, here is the output of some commands related to audio hardware and software:
trin@Trinity:~$ uname -a
Linux Trinity 5.11.0-18-generic #19-Ubuntu SMP Fri May 7 14:22:03 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
trin@Trinity:~$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: NVidia [HDA NVidia], device 3: HDMI 0 [HDMI 0]
  Subdevices: 0/1
  Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 7: HDMI 1 [HDMI 1]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 8: HDMI 2 [HDMI 2]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 9: HDMI 3 [HDMI 3]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 10: HDMI 4 [HDMI 4]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 11: HDMI 5 [HDMI 5]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 12: HDMI 6 [HDMI 6]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: Generic [HD-Audio Generic], device 0: ALC1220 Analog [ALC1220 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: Generic [HD-Audio Generic], device 1: ALC1220 Digital [ALC1220 Digital]
  Subdevices: 0/1
  Subdevice #0: subdevice #0
card 2: U192k [UMC404HD 192k], device 0: USB Audio [USB Audio]
  Subdevices: 0/1
  Subdevice #0: subdevice #0
trin@Trinity:~$ arecord -l
**** List of CAPTURE Hardware Devices ****
card 1: Generic [HD-Audio Generic], device 0: ALC1220 Analog [ALC1220 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: Generic [HD-Audio Generic], device 2: ALC1220 Alt Analog [ALC1220 Alt Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: U192k [UMC404HD 192k], device 0: USB Audio [USB Audio]
  Subdevices: 0/1
  Subdevice #0: subdevice #0
card 3: C920 [HD Pro Webcam C920], device 0: USB Audio [USB Audio]
  Subdevices: 0/1
  Subdevice #0: subdevice #0
trin@Trinity:~$ inxi -SA
System:    Host: Trinity Kernel: 5.11.0-18-generic x86_64 bits: 64 Desktop: GNOME 3.38.4 Distro: Ubuntu 21.04 (Hirsute Hippo) 
Audio:     Device-1: NVIDIA TU106 High Definition Audio driver: snd_hda_intel 
           Device-2: Advanced Micro Devices [AMD] Starship/Matisse HD Audio driver: snd_hda_intel 
           Device-3: Logitech OrbiCam type: USB driver: snd-usb-audio,uvcvideo 
           Device-4: BEHRINGER UMC404HD 192k type: USB driver: snd-usb-audio 
           Sound Server: ALSA v: k5.11.0-18-generic 
trin@Trinity:~$ lspci -nnk | grep -A 1 Audio
2d:00.1 Audio device [0403]: NVIDIA Corporation TU106 High Definition Audio Controller [10de:10f9] (rev a1)
    Subsystem: Gigabyte Technology Co., Ltd TU106 High Definition Audio Controller [1458:37c2]
    Kernel driver in use: snd_hda_intel
--
2f:00.4 Audio device [0403]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse HD Audio Controller [1022:1487]
    Subsystem: Micro-Star International Co., Ltd. [MSI] X570-A PRO motherboard [1462:9c37]
trin@Trinity:~$ cat /proc/asound/cards
 0 [NVidia         ]: HDA-Intel - HDA NVidia
                      HDA NVidia at 0xf7080000 irq 72
 1 [Generic        ]: HDA-Intel - HD-Audio Generic
                      HD-Audio Generic at 0xf7900000 irq 74
 2 [U192k          ]: USB-Audio - UMC404HD 192k
                      BEHRINGER UMC404HD 192k at usb-0000:2a:00.1-2, high speed
 3 [C920           ]: USB-Audio - HD Pro Webcam C920
                      HD Pro Webcam C920 at usb-0000:2a:00.1-6.1.4, high speed
trin@Trinity:~$ sudo lshw -C multimedia
  *-usb:1                   
       description: Audio device
       product: UMC404HD 192k
       vendor: BEHRINGER
       physical id: 2
       bus info: usb@1:2
       version: 1.12
       capabilities: usb-2.00 audio-control
       configuration: driver=snd-usb-audio maxpower=500mA speed=480Mbit/s
  *-usb:3
       description: Video
       product: HD Pro Webcam C920
       vendor: Logitech, Inc.
       physical id: 4
       bus info: usb@1:6.1.4
       version: 0.19
       serial: 47963BFF
       capabilities: usb-2.00
       configuration: driver=snd-usb-audio maxpower=500mA speed=480Mbit/s
  *-multimedia
       description: Audio device
       product: TU106 High Definition Audio Controller
       vendor: NVIDIA Corporation
       physical id: 0.1
       bus info: pci@0000:2d:00.1
       version: a1
       width: 32 bits
       clock: 33MHz
       capabilities: pm msi pciexpress bus_master cap_list
       configuration: driver=snd_hda_intel latency=0
       resources: irq:72 memory:f7080000-f7083fff
  *-multimedia
       description: Audio device
       product: Starship/Matisse HD Audio Controller
       vendor: Advanced Micro Devices, Inc. [AMD]
       physical id: 0.4
       bus info: pci@0000:2f:00.4
       version: 00
       width: 32 bits
       clock: 33MHz
       capabilities: pm pciexpress msi bus_master cap_list
       configuration: driver=snd_hda_intel latency=0
       resources: irq:74 memory:f7900000-f7907fff
trin@Trinity:~$ dpkg -l | grep alsa
ii  alsa-base                                                   1.0.25+dfsg-0ubuntu7                                                 all          ALSA driver configuration files
ii  alsa-firmware-loaders                                       1.2.2-1                                                              amd64        ALSA software loaders for specific hardware
ii  alsa-source                                                 1.0.25+dfsg-0ubuntu7                                                 all          ALSA driver sources
ii  alsa-topology-conf                                          1.2.4-1                                                              all          ALSA topology configuration files
ii  alsa-ucm-conf                                               1.2.4-2ubuntu1.1                                                     all          ALSA Use Case Manager configuration files
ii  alsa-utils                                                  1.2.4-1ubuntu3                                                       amd64        Utilities for configuring and using ALSA
ii  alsamixergui                                                0.9.0rc2-1-10ubuntu1                                                 amd64        graphical soundcard mixer for ALSA soundcard driver
ii  gstreamer1.0-alsa:amd64                                     1.18.4-1                                                             amd64        GStreamer plugin for ALSA
ii  libalsaplayer-dev                                           0.99.81-2build2                                                      amd64        alsaplayer plugin library (development files)
ii  libalsaplayer0:amd64                                        0.99.81-2build2                                                      amd64        alsaplayer plugin library
ii  libclalsadrv-dev                                            2.0.0-3.1                                                            all          ALSA driver C++ access library (development files)
ii  libclalsadrv2                                               2.0.0-3.1                                                            amd64        ALSA
trin@Trinity:~$ cat /etc/pulse/default.pa
#!/usr/bin/pulseaudio -nF
#
# This file is part of PulseAudio.
#
# PulseAudio is free software; you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# PulseAudio is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.
# This startup script is used only if PulseAudio is started per-user
# (i.e. not in system mode)
.fail
### Automatically restore the volume of streams and devices
load-module module-device-restore
load-module module-stream-restore
load-module module-card-restore
### Automatically augment property information from .desktop files
### stored in /usr/share/application
load-module module-augment-properties
### Should be after module-*-restore but before module-*-detect
load-module module-switch-on-port-available
### Use hot-plugged devices like Bluetooth or USB automatically (LP: #1702794)
.ifexists module-switch-on-connect.so
load-module module-switch-on-connect
.endif
### Load audio drivers statically
### (it's probably better to not load these drivers manually, but instead
### use module-udev-detect -- see below -- for doing this automatically)
#load-module module-alsa-sink
#load-module module-alsa-source device=hw:1,0
#load-module module-oss device="/dev/dsp" sink_name=output source_name=input
#load-module module-oss-mmap device="/dev/dsp" sink_name=output source_name=input
#load-module module-null-sink
#load-module module-pipe-sink
### Automatically load driver modules depending on the hardware available
.ifexists module-udev-detect.so
load-module module-udev-detect
.else
### Use the static hardware detection module (for systems that lack udev support)
load-module module-detect
.endif
### Automatically connect sink and source if JACK server is present
.ifexists module-jackdbus-detect.so
.nofail
load-module module-jackdbus-detect channels=2
.fail
.endif
### Automatically load driver modules for Bluetooth hardware
.ifexists module-bluetooth-policy.so
load-module module-bluetooth-policy
.endif
.ifexists module-bluetooth-discover.so
load-module module-bluetooth-discover
.endif
### Load several protocols
.ifexists module-esound-protocol-unix.so
load-module module-esound-protocol-unix
.endif
load-module module-native-protocol-unix
### Network access (may be configured with paprefs, so leave this commented
### here if you plan to use paprefs)
#load-module module-esound-protocol-tcp
#load-module module-native-protocol-tcp
#load-module module-zeroconf-publish
### Load the RTP receiver module (also configured via paprefs, see above)
#load-module module-rtp-recv
### Load the RTP sender module (also configured via paprefs, see above)
#load-module module-null-sink sink_name=rtp format=s16be channels=2 rate=44100 sink_properties="device.description='RTP Multicast Sink'"
#load-module module-rtp-send source=rtp.monitor
### Load additional modules from GSettings. This can be configured with the paprefs tool.
### Please keep in mind that the modules configured by paprefs might conflict with manually
### loaded modules.
.ifexists module-gsettings.so
.nofail
load-module module-gsettings
.fail
.endif
### Automatically restore the default sink/source when changed by the user
### during runtime
### NOTE: This should be loaded as early as possible so that subsequent modules
### that look up the default sink/source get the right value
load-module module-default-device-restore
### Make sure we always have a sink around, even if it is a null sink.
load-module module-always-sink
### Honour intended role device property
load-module module-intended-roles
### Automatically suspend sinks/sources that become idle for too long
# Uitgecommentarieerd om te voorkomen dat mijn speakers klikken
#load-module module-suspend-on-idle
### If autoexit on idle is enabled we want to make sure we only quit
### when no local session needs us anymore.
.ifexists module-console-kit.so
load-module module-console-kit
.endif
.ifexists module-systemd-login.so
load-module module-systemd-login
.endif
### Enable positioned event sounds
load-module module-position-event-sounds
### Cork music/video streams when a phone stream is active
load-module module-role-cork
### Block audio recording for snap confined packages unless they have
### the "pulseaudio" or "audio-record" interfaces plugged.
.ifexists module-snap-policy.so
load-module module-snap-policy
.endif
### Modules to allow autoloading of filters (such as echo cancellation)
### on demand. module-filter-heuristics tries to determine what filters
### make sense, and module-filter-apply does the heavy-lifting of
### loading modules and rerouting streams.
load-module module-filter-heuristics
load-module module-filter-apply
### Make some devices default
#set-default-sink output
#set-default-source input