WIREGUARD & MIKROTIK --> NextDNS Possible?

Good day,  currently using a Mikrotik container for Adguard.   This is used for three vlans that go out a MULLVAD 3rd party VPN, lets say Sweden.   The only 'weird' requirement is to ensure I  point the adguard to the DNS provided by mulvad.   This is done so that the adguard does not make use of the local WAN to establish the secure connection to adguard servers but  so that the adguard goes through the wireguard tunnel and out the mullvad location to make the initial connection.     Yes, we can easily use NextDNS over the DOH certificate setting within Mikrotik for the rest of the routers  needs (subnets going out local WAN).

The problem is I dont see a way of pointing the NextDNS software out the wireguard tunnel for DNS, using the supplied mullvad DNS.     It appears to be different than adguard or pihole in this regard.   Unique requirements so to speak that do not seem compatible with what we wish to achieve.   

Has anyone achieved success sending next dns out 3rd party VPN as discussed above and if so  how?

Is there an official NextDNS container or docker that is "arm" friendly that works like adguard for example??