I use an Amazfit GTR 2e, and it works almost perfectly with gadgetbridge. The only difficulty I have is i’m unable to manually update A-GPS data, so getting a GPS lock can take a while. But I don’t use it a lot, and honestly, the Fitbit Versa I came from wasn’t all that much better.
I used syncthing for a while. Then tried github with mostly terrible results. Now i’m back on syncthing. It involves a little bit of setup, but i mostly forget about it now. It just works.