I had a similar problem on a closed LAN with no internet connection. iOS 16.x devices cannot find their peers.
Entering the IP address and port number individually can help, but it is not a fundamental solution.
Please Resilio Sync iOS developers. Please apply to Apple for a com.apple.developer.networking.multicast entitlement.
https://developer.apple.com/news/?id=0oi77447
Regards,