I am running Endeavour OS on my laptop and I need to connect to my OPNSense through wireguard, but the performance has been terrible, DNS resolution to be precise. I think this is related to a specific configuration to either NetworkManager or openresolv, because the same configuration file works fine on Android or Windows devices.
My suspicions are that because I am using two piholes that are on the same network of the OPNSense router (and I have a few firewall rules redirecting every DNS traffic to them), there is a conflict somewhere.
I have also tried to mess around with the MTU size, but to no avail.
I was dealing with wire guard dns issues recently. What is the interface set to in settings > DNS? I had to set mine to permit all origins for pihole to play nice with wireguard.