Update /etc/systemd/resolved.conf and add some DNS servers (in this example, 1.1.1.1 is CloudFlare, and 8.8.8.8 and 8.8.4.4 are Google but you can use your preferred DNS servers.)
[Resolve]
DNS=1.1.1.1 8.8.8.8
FallbackDNS=8.8.4.4
Restart system resolved:
service systemd-resolved restart
Run resolvectl status (or systemd-resolve --status in older versions of systemd) to see if the settings took.
If they don’t take after a reboot, there’s something else going on.
You can’t fool me, they have another daemon for that