I'm using NextCloud for that. Nextcloud can be basically used in local-first mode (mimicking dropbox). My phone automatically uploads all pictures to the NextC

I'm using NextCloud for that. Nextcloud can be basically used in local-first mode (mimicking dropbox). My phone automatically uploads all pictures to the NextCloud. Then there are apps. For instance I use Nextcloud with the Music app to stream my own mp3s from my Nextcloud to my phone running Ampache. There are also collaborative editing tools, and various options to edit all sort of documents in a web UI, and always the local editing fallback (or the opposite way, as you see fit).