I’ve encountered a similar issue with WireGuard on my iOS and macOS devices. On iOS, I need to first connect to the VPN, then disable and re-enable both Wi-Fi and cellular data before the traffic begins flowing through the tunnel. On macOS, the process involves connecting the tunnel and toggling Wi-Fi off and on. It seems like I have to reset the network connection on the device after establishing the tunnel to get it working. I’m also using OPNsense with the WireGuard plugin.

Sounds like it may be the same issue so I hope that this helps!