I tried every "trick" / "workaround" - nothing works. Not even going Offline to try and keep the save on local storage - it resets as soon as it detects online connection (which is needed for updates, purchases, online games, etc) which is a ridiculous option anyway to stay offline for just one game. Xbox seem to be on holidays now too so we're unlikely to resolve this until they update firmware that addresses this specific issue.
xbox series x firmware still sitting on 2921
bg3 now at 1.5.4