I once invested some time into integrating Syncthing as a library into my GUI wrapper. I also had in mind to port it to Android. However, I was blocked by Refactor out cmd/syncthing · Issue #4085 · syncthing/syncthing · GitHub. And besides, I’m still not sure whether it is worth it in the end.
I usually just use Syncthing for small directories which can be on the internal storage as well. For the camera “send-only” is good enough. Other things like movies and music is just copied or accessed from my server via SMB or KDE connect.