It's a minor issue that we had with Dnsmasq, but we've run into this issue and documented it, so you don't have to
"Dnsmasq does not start because port 53 is busy"
https://blog.zero-iee.com/en/posts/dnsmasq-startup-error-with-systemd-resolved/
@zeroiee this is incomplete. systemd-resolved runs on address 127.0.0.53. just use listen-address=127.0.0.1 and bind-interfaces to listen also on localhost. Add interface for any other interface or additional listen-address=::1