I am interested if there is a solution for this problem. My use case is a peer to peer VoIP application, when there is no server at all.

It is possible, but the connection time might be very long if the 2 peers are not on the same network. If both are on the same network (LAN), then the connection time is fast and the communication protocol is simpler (e.g. SIP protocol is essentially a peer to peer protocol and VoIP applications can be implemented using for example PJSUA.). When the peers are in different networks (e.g. both are in different LANs behind firewalls with access to Internet) a possible solution is to use BitTorrent Bleep

I have discussed with Apple technical support about this. At this moment it seems that VoIP applications in background can receive incoming calls by using either a public or a private push notifications server. https://developer.apple.com/documentation/networkextension/local_push_connectivity?language=objc I have opened a feedback with Apple for this: https://feedbackassistant.apple.com/feedback/9386479

I had to downgrade Xcode to 12.5.1 in order to be able to load the provisioning profile and sign the application. The provisioning profile cannot be loaded by Xcode 13.0