Can I use both systemd-networkd and NetworkManager, or is there an GUI/ncurses alternative to Network Manager?

I am getting used to netplan.io on my laptop after routinely uninstalling it for several years in favor of ifupdown.

This is probably far-fetched, but since it's running a desktop front-end (plasma), I'm wondering if it'd be possible to use it to use two different renderers simultaneously - one for ethernet, and one for wifi, as I have failed to find a GUI for systemd-networkd, but would still like to be able to configure the wifi with a GUI.

Example:

"network": {
  "version": 2,
  "renderer": "networkd",
  "ethernets": {
    "enp0s31f6": {
      "dhcp4": false,
      "addresses": [
        "192.168.1.28/24"
      ],
      "routes": [
        {
        "to": "default",
        "via": "192.168.1.1"
        }
      ],
      "nameservers": {
        "addresses": [
          "192.168.1.2", "192.168.1.3"
        ],
        "search": [
          "domain.com"
        ]
      },
      "dhcp6": true
    }
  },
  "wifis": {
    "wlan0": {
      "renderer": "NetworkManager"
    }
  }
}

(I've been writing my configs in JSON and converting them with yq, since I like how JSON is a bit more explicit)

If it is impossible to use two renderers at once, is there an alternative to NetworkManager but has a similar interface that uses ncurses or Qt, and will interact with wlan0 on systemd-networkd?

I came across Intel's connman package, which appears to work just fine, and there is a Qt interface package for it called cmst.

I didn't think it would work with systemd-networkd, but it let me join the local wifi network without any issues, and it is in fact controlling the configuration of systemd-networkd, as evidenced by its unit file:

$ sudo systemctl status systemd-networkd
● systemd-networkd.service - Network Configuration
     Loaded: loaded (/lib/systemd/system/systemd-networkd.service; enabled; vendor preset: enabled)
     Active: active (running) since Mon 2022-01-31 23:04:42 PST; 22h ago
TriggeredBy: ● systemd-networkd.socket
       Docs: man:systemd-networkd.service(8)
   Main PID: 4537 (systemd-network)
     Status: "Processing requests..."
      Tasks: 1 (limit: 23746)
     Memory: 2.0M
        CPU: 5.559s
     CGroup: /system.slice/systemd-networkd.service
             └─4537 /lib/systemd/systemd-networkd

Feb 01 20:49:59 treygouty systemd-networkd[4537]: br-int: Gained carrier
Feb 01 20:50:00 treygouty systemd-networkd[4537]: ovs-system: Gained IPv6LL
Feb 01 20:50:00 treygouty systemd-networkd[4537]: br-int: Gained IPv6LL
Feb 01 20:50:02 treygouty systemd-networkd[4537]: enp0s31f6: Gained carrier
Feb 01 20:50:03 treygouty systemd-networkd[4537]: enp0s31f6: Gained IPv6LL
Feb 01 20:50:04 treygouty systemd-networkd[4537]: enp0s31f6: DHCPv6 address redacted/128 (valid for 4h, preferred for 2h 30min)
Feb 01 20:52:33 treygouty systemd-networkd[4537]: wlan0: Link UP
Feb 01 20:53:57 treygouty systemd-networkd[4537]: wlan0: Connected WiFi access point: happyhut (86:2a:a8:88:b5:21)
Feb 01 20:53:57 treygouty systemd-networkd[4537]: wlan0: Gained carrier
Feb 01 20:53:58 treygouty systemd-networkd[4537]: wlan0: Gained IPv6LL

connman appears to be a decent connection manager in its own right, with a CLI helper named connctl - here's the identification of the technologies, and a sampling of its CLI monitor:

$ for i in state technologies monitor; do connmanctl $i; done
  State = online
  OfflineMode = False
  SessionMode = False
/net/connman/technology/p2p
  Name = P2P
  Type = p2p
  Powered = False
  Connected = False
  Tethering = False
/net/connman/technology/ethernet
  Name = Wired
  Type = ethernet
  Powered = True
  Connected = True
  Tethering = False
/net/connman/technology/wifi
  Name = WiFi
  Type = wifi
  Powered = True
  Connected = True
  Tethering = False
  TetheringIdentifier = redacted
/net/connman/technology/bluetooth
  Name = Bluetooth
  Type = bluetooth
  Powered = False
  Connected = False
  Tethering = False
Manager      ServicesChanged      = {
unchanged                ethernet_c85b763c1a3d_cable
unchanged                ethernet_4e09c1a325ae_cable
unchanged                ethernet_7ab3c8ed895b_cable
unchanged                wifi_e4b318e0de7c_6861707079687574_managed_psk
unchanged                wifi_e4b318e0de7c_7866696e69747977696669_managed_none
unchanged                wifi_e4b318e0de7c_4d4f544f37464441_managed_psk
unchanged                wifi_e4b318e0de7c_4e4554474541523430_managed_psk
}, {
removed                  /net/connman/service/wifi_e4b318e0de7c_466c61707079_managed_psk
removed                  /net/connman/service/wifi_e4b318e0de7c_73616c6f6e333630_managed_psk
removed                  /net/connman/service/wifi_e4b318e0de7c_hidden_managed_ieee8021x
removed                  /net/connman/service/wifi_e4b318e0de7c_536861726a6f77696669_managed_psk
removed                  /net/connman/service/wifi_e4b318e0de7c_hidden_managed_psk
}
Manager      ServicesChanged      = {
unchanged                ethernet_c85b763c1a3d_cable
unchanged                ethernet_4e09c1a325ae_cable
unchanged                ethernet_7ab3c8ed895b_cable
unchanged                wifi_e4b318e0de7c_6861707079687574_managed_psk
}, {
removed                  /net/connman/service/wifi_e4b318e0de7c_4d4f544f37464441_managed_psk
removed                  /net/connman/service/wifi_e4b318e0de7c_7866696e69747977696669_managed_none
removed                  /net/connman/service/wifi_e4b318e0de7c_4e4554474541523430_managed_psk
}

But the GUI was what I was really after. Despite not looking all that slick, it actually appears to have access to quite a few more features than NetworkManager typically would:

So, there you have it. Nice to know there's an alternative!

Yes, it is possible to use NetworkManager for one set of interfaces and networkd for another. As documented at https://netplan.io/reference/:

renderer (scalar)
  Use the given networking backend for this definition. Currently
  supported are networkd and NetworkManager. This property can be
  specified globally in network:, for a device type (in e. g.
  ethernets:) or for a particular device definition. Default is
  networkd.

While not explained there, if you have multiple interfaces of each type, it is possible to have a separate file for each renderer and declare the renderer: at the top level within the file so that you don't have to repeat it for each interface.