If anyone, using Fedora Linux 42, has issues with OBS-Studio and the Virtual-Camera mode:
That's because of an incompatibility between OBS-Studio 31.0 and the v4l2loopback Kernel module in version 0.14.0.
The fix for that is in obs 31.0.3, which is on the way from testing to stable right now. Should be offered as an RPM update within the next days.
Fedora Bugfix Update:
https://bodhi.fedoraproject.org/updates/FEDORA-2025-85fcdbf461
Upstream Bug: https://github.com/obsproject/obs-studio/issues/11891