@wifird1 and @zimo, although it has now been quite a bit since you posted, I suspect you may find resolution (or, at the very least, the tools you need to configure things to your liking) in this thread:
Solution 1, tweaking things so there are no DNS leaks when connected to a VPN client, but not using AdGuard Home when on VPN: Sharing a solution for DNS leak with AdGuard Home handling client requests + connecting to VPN client
Solution 2, tweaking things so you can still use AdGuard Home while connected to a VPN client without DNS leaks: Sharing a solution for DNS leak with AdGuard Home handling client requests + connecting to VPN client - #16 by Integritas
If you're mainly interested in Solution 2, after clicking the link above, scroll to the portion of that post that says
And, depending on which way you go, you may also be interested in this post where a person asked me about upstream DNS servers within AdGuard Home: Sharing a solution for DNS leak with AdGuard Home handling client requests + connecting to VPN client - #7 by Integritas
I hope this helps!