The only time I have compiled a kernel in the last 10 years was to bisect to determine what change introduced a bug affecting my particular hardware combination.

Are you sure L2 is 192.168.1.0/24 and not something larger that includes 192.168.30.0, e.g.: 192.168.0.0/16?

What does ip route show before and after connecting to WG?

Are you testing DNS via dig @<nameserver>? or just with ping? Are you running systemd-resolved?

Yet another critical vulnerability in systemd

This is a critical vulnerability in snapd, not systemd. It sounds like it could also be exploited if something other than systemd deleted the files in /tmp/. Or if /tmp/ was not mounted.