Yeah I also wasn't that impressed with Nextcloud mobile. I ended up using Syncthing instead, adding the DCIM/Camera folder as a sync folder works like charm.
Discussion
Syncthing is really great. We used that to sync obsidian notes.
We wanted a nice photo app to work with photos on the phone, and somewhere else. So we decided to use nextcloud instead. The Memories app is quite nice.
Probably somehow solvable with synchting too. But not really its purpose.
If sync is okay, nextcloud is quite decent for photo storage.