I mean I’ll give it a try, their support flat out said they don’t support port forwarding for WireGuard configs which is why I never used the feature, but if it’s truly using UPnP than it may be worth a shot!

As for router setups, the Port Forwarding feature is unfortunately not yet officially tested and supported, therefore, I will be unable to provide any specific steps for setting it up and creating a port mapping on your Asus router, nor guarantee that this specific scenario would work as intended. Our team will consider testing it on router setups as well in the future, however, at this moment, I am unable to provide any specific time-frames or further details. I apologize for the inconvenience that this may cause you.

Edit: https://protonvpn.com/support/port-forwarding-manual-setup#wireguard looks promising!