Re: Errr but...
Ubuntu seem to be trying to bring some sanity to the systemd - gnome ghastliness, with the introduction of netplan. This seems to be a tool that you use to specify how you want network configuration to work in some file, run netplan, and it stamps out the corresponding config files for systemd and networkmanager.
Yes, networking has gone even more meta. Now you configure something that configures other things that will in turn configure yet more things. And of course, this all means that things that were possible in the past are now not possible...
BTW Ubuntu 20.04 seems to come with both NetworkManager and systemD configured to think that they're controlling DNS. I think that systemD mostly wins, but it has caused me no end of trouble in some domains. These were all sorted by telling NetworkManager to not fiddle with dns settings by adding "dns=none" to its configuration and leaving systemd resolveD stock / enabled.
Rant
SystemD's resolved seems particularly objectionable. The apparent intention behind it is that applications will name resolve using dBus calls into resolveD, whilst it provides a bastardised /etc/resolv.conf for "legacy" applications. How can name resolution via dbus ever be a good idea, all things considered? The implication is that at some point they'll deprecate /etc/resolv.conf altogether, and then name resolution in a system will be entirely dependent on a whole bunch of daemons being properly configured and running. Surely that'd be an insane position to be in?
Why is it that Linuxes, of all the major OSes out there, seems to be the only one that has these tortuous, competing and often conflicting problems with DNS, and with networking in general? I can't even begin to remember the last time I saw a Windows or Mac or OS/2 machine get its DNS config in a twist.
What's worse is that both NetworkManager and systemD are essentially from the same stable - RedHat / LP - and they've managed to foist this entire shit shower off onto more or less the entire Linux world.
Don't get me started on automounteD vs autofs...