I do - Syncthing runs on both Linux (my PC) and Android (my phone). The configuration is same as any syncthing setup to share a folder (the top-level folder containing all the Obsidian vaults in this case) between two nodes (my PC and phone in this case) - their UI[0] is relatively straightforward.
Obsidian has an optional paid sync plugin that works out of the box. You could use Syncthing but I don't think it does text file diffing? Obsidian Sync keeps a version history of each file
I have tried to use a plugin called Obsidian Git that automatically runs git commits and pushes on an interval, but I have found it frequently had conflicts and the visual for resolving those conflicts wasn't super helfpul. I ended up just paying for Obsidian Sync. I wish I had a solution that kept my data just to myself, but I don't care that much of Obsidian has my notes
For my notes, it is only me who edits, so I don't have conflicts as such. If I edit notes on the phone while on the move, syncthing syncs to PC once I'm back home; similarly any changes done at home on the PC flow to the phone. I also use the Obsidian Git plugin (though I have disabled automatic commits and commit as and when I feel the need) - haven't had any conflicts so far.
It's also only me editing my notes and I have Obsidian git conflicts all the time.
Also, it freezes my typing every time it tries to push/pull. So if you put it on an interval, to make it more automatic, your typing will just be frozen every however many seconds
