ProtonVPN foibles: ALWAYS remove old protonvpn completely before installing.
tells you what DNS servers will be used to overwrite /etc/resolv.conf by systemd.
In /etc/systemd/resolved.conf set the following just after the [resolve] keyword:
/etc/resolvconf/resolv.conf.d/tail maybe should contain:
What does this latter do? It seems to concatenate the line after whatever is written into /etc/resolv.conf. I dont know if that makes any difference. It should be BEFORE the line
if it is to have any effect in giving search precedence over the 127.0.0.53.