I remember that android has "hardcoded" the dns server to be your home ISP router's, that's probably what's causing the dns leak.
On your phone's wireguard config add the following DNS server: 9.9.9.9
Or change your private DNS in your connection settings on your phone to: dns.quad9.net. This won't work with wireguard.
I followed a similar tutorial to route all my devices traffic to ProtonVPN and it's miles away of being that complicated, but I have no idea what's your actual use case.
Also, you have to allow all traffic to your client's wireguard tunnel: 0.0.0.0/0.
Hope it helps !
Edit: Ohh it's a wireguard docker server... If I were you, I wouldn't bother to use wireguard in a container... Just install it bare bone on your server !
Edit2: Maybe I'm wrong, but docker containers uses the host's DNS, so this could also be a bad DNS configuration on your host !
Sorry can't see your image, javascript blocked, but reading through your link I suppose you want to route all your traffic from all your devices to ProtonVPN from your host server/wireguard.
I have something similar and followed the following general guidelines: Wireguard VPN endpoint.
While this doesn't solve your DNS problem, I can vouch for the guidelines working on my side (bare bone not in a container). Having all my traffic being routed to my wireguard server and accessing all my containers without DNS leaks.