Syncthing is working well for photos, .kdbx database and a few random test files. Baïkal is working with DAVx5 to sync my contacts and calendar to my Pixel 8 running GrapheneOS. Haven't got notes syncing yet. But these few things are all I really need synced to mobile.
NextCloud is a dumpster fire. Syncthing is an unsung hero.
Found any good options for tasks/projects?
Discussion
I believe I figured out how sync notes from Android via NotallyX. I'll find out if I can open them on PC and edit + sync in a few hours. As far as tasks go, that can be handled with Baïkal or any other CalDav+CardDav server. I'm sure you could technically do so with Syncthing but I took the easy way.