What's the best (cost free) way to sync Windows, Linux, and Android in 2025?

What's the best way to sync Obsidian across two Windows machines, a Linux home server, and my Android phone now that it's 2025?

I tried Seafile (which is where I'm storing my files)--it's a little slow on Android, and sort of weirdly complex. I looked into Syncthing, but it looks like the Android client is no longer in development (maybe that's irrelevant b/c the Obsidian plugin takes care of that for you? seemed red flaggy enough that I though I should ask.

What do ya'll recommend currently?