The commercial VPN client part shouldn’t affect your problem if I’m reading it correctly and you just want to access your LAN remotely. If you’re hosting the Wireguard server on the router, you’ll likely need a firewall rule for the port used by the wg server to allow inbound connections. And you need to configure AllowedIPs correctly on both server and client. And since you’re using OpenWRT, you might try out Policy-based Routing which gives you a lot of control over this and also has some instructions for various server and client configs which may be helpful.

Also, if your ISP uses a CG-NAT you won’t be able to do this, although some will disable it if asked.