Thank you for reaching out to the Zoom Developer Forum. I’ll start by saying that as this forum is dedicated to Zoom Meetings Web Client SDK your question falls outside the scope of our support.
However, I happen to be familiar with this topic so I’ll do my best to help out. First, you’re correct in that GCam is limited to 12MP output.
When you digitally zoom in with your 48MP main shooter, my understanding is that it crops in on the 48MP image to 12MP and then digitally zooms in the extra 2X. Although, I’m not positive what scaling it processing it applies here.
Ultimately, my only experience with this behavior is with a OnePlus 6T on Android 10 which is prior to many of the restrictions that were put in place. One of the experts in the matter, Celso Azevedo, wrote up a great post about this:
If you want confirmation on how GCam handles this, they might be able to advise. I would perform some testing on your end to see if you can confirm the behavior. If not, you can reach out them via their contact form here.
I hope that helps! Happy Modding!