Nextcloud photos are displayed as folders. Pictures on the phone (and SD) are put together into one “stream”. But it would be nice to get the option to display pictures on the phone also in a folder view. Simple Gallery Pro (https://f-droid.org/packages/com.simplemobiletools.gallery.pro - yes, that’s android) might be worth a look for some design feature impressions, or the Pictures/Photos app of Windows 10 Mobile.