Be careful with the automatic setting, it could mess up things badly.
I had Surfshark Wireguard client for one device, all other devices were randomly served by its DNS server which resolves some major sites (bbc/reddit/netflix…) to the same non-existing IP.
Took me days to figure this out.
Enabling Adguard Home doesn’t play well with this, disabling it will reset it to automatic again.
Mine is Automatic and shows the WireGuard DNS server in the list, yet NOTHING uses it - not the router and not clients behind the router. I can force it manually with nslookup on the client, but the dnsmasq instance on the router is NOT forwarding requests to WireGuard when the tunnel is up.