If I look into the Github description of Gallery it says:
Per album design, description and copyright statement
I guess the expection of most people is, like mine too, that they can manage these things in the Nextcluod web GUI. It took me a long time till I discovered, that this is not the case and I found the Galllery configuration. Don’t get me wrong, but this is pretty unhandy for practical daily usage. I think anyone who is interested in photo management would like to set these picture properties individuality and interactivly per photo (or multiple pictures) not only by album. Another much missed feature is the option to display the EXIF data of a picture.
Those improvments would make Nextcloud much more attractive for photographers.
My main intention was, to point out, that the GUI of the Gallery App is missing a lot of picture management features, which you would exspect. In this context the Apps you have mentioned are helpful, but they do not solve the main issue, because their functionallity should integrated in the Gallery App.
I am not at all a developer, just a simple user; so take what follows with a bit of caution.
My impression is that the gallery app is not actively developed.
Possibly the functionality you are looking for could be met by using the Files grid view of Nextcloud 15 plus the sidebar with the Metadata app installed plus the file preview functionality.
try to explain in detail all the functionalities that you need and push for their integration in the server (push through feature requests and / or bounties)
try to propose a new app and again advocate for it
try to develop something by yourself
Take into account that a good feature requests with a reasonable explanation of why it is needed and how it should work could be the right incentive for a developer
I’m sorry if my explanation was too detailed and obvious for you…