I have not used Google Photos in some years, but miss the ability to easily find and browse photos from many years. I know there are a few great looking self-hosted replacements: Immich, Photoprism, etc. However I am unable to selfhost and prefer not to pay for server.
Ideally I would like to just use an rclone remote as the photo repository, however I am unaware of an android app that can do it well.
Some possible solutions:
Use rclone mount: Requires root and not straightforward to setup
And therein lies a fundamental problem with round sync.
I've scoured the app and I can find no way to add rclone command line Flags such as the one that you probably need which is --vfs-cache-mode full.
I'm not certain that even that will help a lot. It's kind of a stretch to be using the app in this manner unfortunately.
My phone Auto uploads all of my pictures to a pcloud drive and the pcloud software lets me on my Android browse my photos the way that I think you want to be able to do with round sync.
Each photo needs to be accessed and downloaded to your phone one at a time and it just doesn't work very efficiently.
So the pcloud app has some sort of thumbnail caching, so you can easily browse through many photos?
Roundsync currently does not have vfs-cache, I'm not entirely clear but it supports some kind of caching, but it does not persist when the app is closed: FR: Offline Cache · Issue #114 · newhinton/Round-Sync · GitHub. Offline persistence probably not necessary if caching was good enough. However I could imagine some solution that keeps a thumbnail database. If only I could use my existing 1GB digikam thumnail database