Earlier quoted context omitted.
What’s your setup for that? How do you sync (incoming) photos to an arbitrary place outside of the Photos library?
I'm not the GP but what I do is all my camera devices will sync to a cloud drive, and my NAS then syncs the cloud drive. Google Photos seems to be able to see them. That way I always have two copies of the image, a cloud version and a local. The main failure mode I'm concerned about is if Google decides I'm no longer worthy of an account. In that case I'll still have my pics and I'll put in the effort to set up some…
With an iPhone it doesn't seem that there is a way to sync with a folder anymore.