GOS-user
I can give you some tips for GrapheneOS and Pixel Camera:
GrapheneOS camera
Triangle top left > Video quality> choose between UHD, FHD, HD and SD.
For photo (not video) you can also reduce the quality in the same menu under more settings> Image Quality.
Frame rate and file format currently (version 66) cannot be set.
Pixel Camera
Open app, tap on video icon then on the gear wheel at the bottom left. Adjust the options "Resolution", "Frames/sec", 10-bit HDR.
Video format can be changed under more settings> advanced> store videos efficiently.
I have not tested this, but "Social media depth features", "Rich color in photos" and "Ulta HDR" could also have an influence on the file size - you would have to test this yourself.
Note: Depending on the device model, not all settings may be available to you.