Cockpit Software Updates - Loading available updates failed - Cannot refresh cache whilst offline

Solution 1:

Apparently Cockpit just 'needs' Network Manager.

That was hinted at in my question as well.

Changing the setting to renderer : NetworkManager makes Cockpit > Software Updates work flawlessly without impacting the Networking module in Cockpit.

Other workarounds cause some modules ( especially the Networking module ) to not function properly. Cockpit project github reference -> https://github.com/cockpit-project/cockpit/issues/15746

Note : This method also ensures that when you use Cockpit to manage your Virtual Machines, creating bridges etc work flawlessly as well.

Solution 2:

According to this, the easiest workaround until Ubuntu settles on a network manager is this:

nmcli con add type dummy con-name fake ifname fake0 ip4 1.2.3.4/24 gw4 1.2.3.1