Even now in Mesa 25.3.3 this issue is not resolved. It happens in the same place. Seems to be an issue with mesa drivers, not proton or the streaming software (WiVRn, ALVR, Steam Link).
So I was able to test it with an old version of WiVRn (v25.6.1 with opencomposite) since it would crash with newer versions. It hang in the very same place. So it's not something due to the VR streaming software. It's so...