Wireguard Selective Routing With Mullvad

[Twixers]

So I have two interfaces with two different networks on two different VLANs. Unfortunately, my Wireguard VPN applies to my single WAN interface, so both networks are on the VPN, although I would like one of them to not be on said VPN. I followed this documentation and reviewed what I did multiple times, but it only cuts everything off the VPN and doesn't work (changing ANY of the Mullvad settings does this, including adding the gateway)

How can I properly use selective routing in a way that will actually work?