Kubuntu 20.04 LTS - Problem with TP-Link Archer T2U Nano AC600

I have Kubuntu 20.04 LTS running like a charm on a (quite old) desktop without wireless card. I have to move this machine in a room that has no wired connection, so I added a USB dongle to get wifi access: TP-Link Archer T2U nano - AC600.

Setting the driver for this model (Realtek chip) is a common thing. but on my PC it didn't work. I first thought the problem was related to the driver, but I finally managed to connect manually, following these instructions.

I now have a connection script

#!/bin/sh
rfkill unblock wlan
wpa_supplicant -B -c /etc/wpa_supplicant.conf -i wlxc006c342ad68
dhclient wlxc006c342ad68

that I have to run with sudo at startup, and after wakeup from sleep mode.

Comments:

• The rfkill is needed to "wake up" the dongle, otherwise the LED stays off and it doesn't work
• 'wlxc006c342ad68' is the local name of the wlan chip

My interpretation is that if the above script works, then there is no problem with the driver. Correct?

One option would be to make this script 'permanent' (I didn't succeed to promote it to a service, as explained in the above link), but it's obviously not the best method. I would prefer to restore the normal functioning of KDE, namely having a network applet in the tray that allows to detect and connect to the wifi.

Actually it seems I have a problem with the network manager: even if the wired connection works without any issue, I don't have any network-related icon in the tray. I can manually add a wireless connection in the GUI of the system configuration / network, but I'm not able to use it.

I tried to reinstall the network manager:

sudo apt remove plasma-nm
sudo apt install plasma-nm

but it didn't change anything.

I solve it following this answer:

sudo apt install git dkms
git clone https://github.com/aircrack-ng/rtl8812au.git  # 2k stars
cd rtl8812au
sudo make dkms_install
reboot  # Just restarting networking.service didn't work

After rfkill and sudo lshw -C network list the device, and inxi -N | grep "TP-Link" now return rtl88XXau instead of usb-network. In my case was an Ubuntu 20.04 with kernel 5.4.x.

The process may take around 10':

$ sudo make dkms_install
mkdir -p /usr/src/8812au-5.6.4.2_35491.20191025
cp -r * /usr/src/8812au-5.6.4.2_35491.20191025
dkms add -m 8812au -v 5.6.4.2_35491.20191025

Creating symlink /var/lib/dkms/8812au/5.6.4.2_35491.20191025/source ->
                /usr/src/8812au-5.6.4.2_35491.20191025

DKMS: add completed.
dkms build -m 8812au -v 5.6.4.2_35491.20191025

Kernel preparation unnecessary for this kernel.  Skipping...

Building module:
cleaning build area...
'make' -j4 KVER=5.4.0-89-generic KSRC=/lib/modules/5.4.0-89-generic/build...................................................................................................................................
Signing module:
- /var/lib/dkms/8812au/5.6.4.2_35491.20191025/5.4.0-89-generic/x86_64/module/88XXau.ko
Secure Boot not enabled on this system.
cleaning build area...

DKMS: build completed.
dkms install -m 8812au -v 5.6.4.2_35491.20191025

88XXau.ko:
Running module version sanity check.
- Original module
  - No original module exists within this kernel
- Installation
  - Installing to /lib/modules/5.4.0-89-generic/updates/dkms/

depmod..........

DKMS: install completed.
dkms status
8812au, 5.6.4.2_35491.20191025, 5.4.0-89-generic, x86_64: installed
bcmwl, 6.30.223.271+bdcom, 4.15.0-161-generic, x86_64: installed
bcmwl, 6.30.223.271+bdcom, 5.4.0-89-generic, x86_64: installed