Comment 2 for bug 1863369

I have also the same problem.
Also in gnome-control-center it shows no internet connection in online accounts.
This problem only occurs when network used for internet connection is not managed by NetworkManager.
There is no problem if I use connection that is managed by NetworkManager (wlp3s0 in my case).

$ LANG= nmcli dev status
DEVICE TYPE STATE CONNECTION
wlp3s0 wifi unavailable --
enp0s31f6 ethernet unmanaged --
lo loopback unmanaged --
...

$ cat /etc/netplan/*.yaml | grep renderer
  renderer: networkd

$ nm-online
Connecting............... 0s [offline]

$ curl -i http://connectivity-check.ubuntu.com/
...
X-NetworkManager-Status: online

$ lsb_release -a
...
Description: Ubuntu Focal Fossa (development branch)
Release: 20.04