> OneDrive ceased to be a good backup alternative when they stripped GPS from all my photos 1-2 years ago.

This is scary. Isn't OneDrive supposed to keep files bit-identical? Or were you using their iOS/Android apps to back up photos, and some bug caused the photos to be backed up without their metadata?

Yes, it is. Although seems only limited to Camera Roll folder. Perhaps this is why Samsung Camera built-in OneDrive integration uses different folder.

Their mobile app is now stripping GPS on upload while files uploaded from desktop are unaffected.

However the files I already had uploaded going back to 2017 were stripped. No idea if this was done server side or by the mobile client but the end effect is the same.

Unlike Google, Microsoft doesn't bother documenting this policy.

I haven't seen this behavior. All of my photos synced from Android to OneDrive have GPS data, as expected. I just checked a few from 2017 (Windows Phone) and 2018 (Android) and still there too. Did you see the same behavior on all your devices?

Looks like it's preserving them now (for newly backed up). I guess I was unlucky.