Well, it's not versioning I need (I have an rsync backup that makes incremental copies). I need a 2-way sync that happens when files changes and doesn't randomly stop working: I want to edit a note on my phone - it copies to the server. Edit on the server, it updates to the phone. Without having to manually run any separate syncs first. I only mention sync conflicts because right now, syncthing hadn't updated with my phone for over 2 days, plenty of time for me to update a note elsewhere and then edit the same note on the phone.

Resilio does it, but it looks like it's draining the battery. Syncthing doesn't drain the battery much, but that's because it has become inactive on two different phones for long periods of time repeatedly.

Cloud provider apps usually work instantly with little drain, they must trigger from OS notifications, but the apps that sync to local servers just don't seem to work that way!

Git is a great solution just for versioning. After I messed up a big note file I had, I set up emacs to hook git into the save function. I just created a repo in that directory, then backed up the whole directory including .git, so the versioning was there with the backup. No need to even use a separate repo, git just gave me a version history for the local files.