WARNING: I'm not a pro at security matters. So this might be an unsafe approach, I'm not sure. And this is limited to game capture
only.
You can configure this by each Sandbox's setting.
You need to open these IPC paths (in the image below) for the game capture hook (which is injected into the game's process, which is running inside the sandbox) to be allowed to send captured frame data (as well as other data necessary for sync ops) to the OBS process outside the sandbox.
[Sample of IPC paths in ini setting, for copypasta geeks]