Chromium <-> Vivaldi connection doesn't seem to work

[dumblob]

Steps to reproduce:

1. install latest Chromium & latest Vivaldi into the same instance running Linux
2. in Chromium open p2p.chat and create a new room (and give permissions to both camera & microphone)
3. copy the Chromium URL and open it in Vivaldi
4. give permissions to both camera & microphone to Vivaldi

In Chromium one can see the camera view and can hear microphone. In Vivaldi camera is (correctly) disabled and one can hear microphone (I'm using pipewire on Linux, so this "shared use of mic" shall work flawlessly).

In Chromium an empty "loading window" will appear in an instant. In Vivaldi as well but a second empty "loading window" will appear shortly after. Notwithstanding both sides will show these loading windows indefinitely with zero progress. I interpret it as they can't connect to each other.

Could this be caused by an asymmetrical NAT which I'm behind? That'd be really bad as I'd like to connect with others from the same LAN. Or is it rather some bigger issue in p2p.chat itself?