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).