You can try to use nextcloud on iOS through web interface. I don’t know how the experience is, for iPads it is perhaps more of an option compared to phones with smaller screens.
For myself, I mostly use the official app to upload photos/videos, not so much to look at them, calendar, contacts. Some apps in Nextcloud have special adapted apps in iOS as well (News, Deck, …)
You could go to the ios-repo and go through the feature requests. For the albums etc. there are certainly a few requests. But if you check the changes in the latest version, or the latest features being pulled, you can see a bit what is going on, what they are working on.
Alternatively, I don’t know if there are any apps for photo management that let you use webdav resources natively, this way you could hook it up to Nextcloud.