Update: Meta has since resolved the issue, please make sure you're on the most up to date version of the Meta software.
Recently Meta pushed an update for their PC client that has broken compatibility with some OpenXR titles including Pavlov. The game will launch in flat screen, but not in the headset. We are in communication with Meta in resolving this issue.
There are some methods players can use to downgrade their versions, but we cannot distribute this software ourselves nor can we recommend downloading older clients from an unverified source.
If you are using a Quest there are alternative streaming methods you can use such as Steam Link, Virtual Desktop, or ALVR. This will require you to change your OpenXR runtime to SteamVR instead of Meta/Oculus.
We appreciate your patience while we work with Meta on resolving this ASAP with an official update for their software.