Thanks @xblax for the details.
Only point I don’t get which seems to be not answered to me is:
Does the e / os / camera have all the other issues/bugs described here apart from the possibility to use the wide angle camera?
In general to deal with that, as long as it not fixed by Fairphone:
Why not using the “e / os / camera” and transform it to a system app for now? (also for other custom roms)
I know there are people which prefer the Gcam (or the ports) in regards of the photo quality, but still, I think Open Camera is a good camera app, which fits, at least to my needs. So is there a place where one can get the “e / os / camera” as apk or do I need to create an APK on my own out of the code in GitLab (never did that up to now but I’m willing to find out)?
Will do. 