Change DNS servers in systemd

This might seem confusing to some but it’s actually quite easy, ignore resolvectl and use nmcli to set a DNS for each connection.

nmcli con mod "my connection" ipv4.ignore-auto-dns yes
nmcli con mod "my connection" ipv4.dns 8.8.4.4,8.8.8.8
nmcli con down "my connection"
nmcli con up "my connection"

Verify with resolvectl.

Change back to DHCP by toggling nmcli con mod "my connection" ipv4.ignore-auto-dns no and restart the connection again.