How do I permanently disable Google Photos pop-up prompt to backup my photos?

Older people (seen it at 65+) will just click the nag without knowing what the button does and end up beaming up all photos to google cloud with no ability to disable the nag (it keeps showing up after a while) even when dismissed. If you are concerned about your data privacy, you may want to check on what photos of say your kids your parents are beaming up to google without their or your knowledge.

The answer in the thread (which is quite hard to find) is to use the Google Photos app without an account.

The app has some very nice features that are locked behind account access though.