I highly recommend NextCloud. It's trivial to set up with Digital Ocean, and I've been using it for a couple of years now without a hiccup. I use it as a file server, calendar, and a media streaming solution.
Syncthing is definitely nice if you just need p2p sync between devices though.
If you need more than that, like a web portal full of your files, sharing via web links, etc.... Try nextcloud.