Configuring dns server with wireguard client

i'm wondering is there a best practice for configuring dns server with wireguard?

the instruction from mulvad says to change the dns on the lan interface.

the instruction from azirevpn says to change the dns on the wan interface.

either way appears to work but is there a right way to configure dns server with a wireguard client?

If you follow the azirevpn approach, then the WG endpoint must be an IP, not a fqdn, unless their nameserver allows queries from outside their network.