IIRC, the wireguard server's config file has defined peers (clients) so you could just remove the peer pubkey from the config file and they would no longer be able to connect.
I have wanted to get my hands on this stuff as a hobbyist computer Builder since about 2015 it's a shame because I live not even a few miles away from 3M Oakdale where the fellow Phil Tuma makes videos of delidded CPUs cranking away submerged in this stuff.