Apple - How can I trick programs to believe that a recorded video is what is captured from my MacBook Pro camera in realtime?

I would suggest installing OBS (Open Broadcaster Software) from this web site:

https://obsproject.com/

It allows you to create content in a variety of ways, including green screens, etc. In your case it is just a simply video you want playing.

If you have the very latest version of OBS a virtual camera plugin is included with the software. If you have an older version, you can download and install the same OBS Virtual Cam plugin from here:

https://github.com/johnboiles/obs-mac-virtualcam

When installed you'll have a VirtualCam option in the Tools menu in OBS, where you can start a virtual camera.

Finally in Google Meet select the virtual camera as your camera. Now the output from OBS is transmitted to meeting partners in Google Meet - and from OBS you can control whether the video is a pre-recorded file, your actual web camera, or something entirely else (like a still photo or similar).

Not a direct answer, since I don't know GoogleMeet, but if you're using Zoom or WebEx, just record yourself through your webcam then use that video as your virtual background. Just be sure to make the video long enough so it loops well.