I will add this in case it's useful for someone. All of my photos (thousands, from phone and camera going back over 20 years) were backed up to MS OneDrive until they said my drive was getting full. So about 10 years ago I switched to a Gmail and now I'm being told my Google storage is at 86% full. I only recently remembered that as a Prime member, I get unlimited photo storage. I made sure everything was set to back up to Prime photo (which it was) and when I'm 100% sure everything, ever, is backed up, then I will delete from my phone and from Google.
If I'm paying for Prime then I might as well use this facility, rather than trying to go through thousands of photos and videos deciding what to delete and what I may want to keep (e.g can't bring myself to delete any pics of my son, even if they're not very good ones).