I'm having similar issues to @El_duderino
Namely, I'm getting video from Blackmagic Camera App on a Pixel 6 Pro which is unusable. I'm recording in 1080p (due to space and bandwidth issues while travelling) and I'm getting noisy/grainy video which is absolutely terrible. It is worst in daylight video (low ISO).
I've tried: HEVC, H264, Reduce Noise on/off, Sharpening on/off, Increased bit rate, Lens correction on/off, 1.0x Lens and Wide Lens.
When we went to make our video and started going through the footage we were shocked at how bad it was, and how inconsistent. Indoor videos seem to fair the best so I thought it was an overheating issue that the Pixel 6 is known for, but taking video out the window from inside an air conditioned apartment shows how bad it is.
I chose not to use the built in camera because it doesn't remember the external mic setting and will always default to the built in mic. I like the interface for the Blackmagic app, especially being able to select the specific lens, but the results are unusable.
Apparently I'm not allowed to post URLs, so here's a single example of some absolute garbage output I got, but it doesn't even show the noise from frame to frame:

- Screenshot 2025-01-26 130153.png (600.66 KiB) Viewed 21827 times
Here's an example with a comparison of the results from the built-in Camera:

- Screenshot 2025-01-26 130456.png (370.45 KiB) Viewed 21827 times

- Screenshot 2025-01-26 131416.png (396.57 KiB) Viewed 21827 times