Hi again.
Think I found the folder, but it is read only: > sudo touch /snap/nextcloud/current/htdocs/installphotosapp.php touch: cannot touch '/snap/nextcloud/current/htdocs/installphotosapp.php': Read-only file system
Solved.
Here is how I did: About what I found
I deleted a lot of photos via the files app, they are still displayed in the Photosapp, what should I do?
there’s no need for “fancy” shell commands, you could have the quickfix installed as a regular app 
though max version is 20 atm
given the pics indeed are deleted try this one via OCC shell
occ files:scan --user
Now I finally updated my server from 17.0.10 to 19.0.4 (with an interim step at 18.0.10 - which failed with DB exceptions, but that’s another story).
I tried to get used to the new photo app - but I can’t 
It’s slow, it misses functionality, it’s inappropriate - to make it short: I still don’t like it.
Even the last incarnations of the gallery app are missing functionality which had been there in earlier versions.
I absolutely miss the integration in the files app - in early versions (when it was “gallery+”) I was able to directly open it in a certain directory - the gallery buttons replaced (or were added) to the right top at each files directory (where the “grid view” button is nowadays).
But even without that functionality, the gallery app is still way better than the photo app!
–> so I deactivated the photo app and readded the old gallery app - I hope it’ll still work in future NC versions!
BTW, when I executed “occ files:scan --all” I also got some exceptions…
…it seems the whole nextcloud code nowadays has lesser quality than earlier versions!
…it seems the whole postings here nowadays have lesser information than earlier postings 
ymmd 
Closing. We’ve been pretty much chatting about everything on this topic and it doesn’t add anything more
Reminders:
- Help about how to use or where to find something are here on this forum
- Features requests and issues are on github!
https://github.com/nextcloud/photos
Thank you all!