I have photo backup turned on but as I believe it should just upload the picture to Proton Drive and that is that.

I see nothing on “offline files” (ie. tap it to make it available offline) so why would it be using 6+GB of storage? I assume it’d be fine to just clear storage and login again but it’s odd that is using so much if it’s not duplicating (I would hope not) my already taken pics from the DCIM directory.