I have same setup, connecting two subnets with own router together by a wireguard connection. I had similar issues, or better I still have it. If I enable a VPN service of one PC this one is not reachable anymore because it switch to another subnet. So you will need to make there a bridge again.
But I am really no IT expert. First I did try it also with OpenVPN but it was not doable at all. Wireguard is much faster and easier to config.
Like with OpenVPN I got only about 5MBit connection, with Wireguard it’s much more.