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This isn't about getting input from a camera (which works fine), but making the output of OBS appear as a camera to the rest of the system.

That's what the above software is for.

My first guess would be a lot of people use OBS for game streaming and a lot of games are Windows-only.

Looking at the OP Windows already have a similar solution. Only macOS doesn't have one.

The OP also wants a similar one for the sound/mic, not only for the video. Also he wants a working solution for non-tech people.

Your example is (from the looks of it) using V4L2 as a source, the linked bounty wants to use V4L2 as a sink.