Turn off Google's auto upload. The entire photos thing has long been a way to get images to train ML, and since they actively use these images you're not in a position of power here. i.e. you're doing Google a favour by using the auto-upload.

Either find a service that you're paying for, or if you want to trust a big corp maybe go with Apple. Not perfect, but best of the lot from what I can see. All of the logic is on-device, so they're less inclined to peek at your photos. There was a big hubbub a while ago when they tried to do unsafe photo detection on-device, but they backtracked.