I gave up and bought it on Steam. (I cancelled my XBox subscription too, fed up with all the issues).
If you rename your FS2020 (or what ever you called it) install folder to FS2020_old before you uninstall it on the Windows Store you can use it on the Steam version. Once uninstalled rename it back to FS2020.
When Steam finishes the 550MB initial install, launch the game, point it to your FS2020 folder and let it start the update and exit the game.
Go into your FS2020 folder and delete the new Steam folder and rename the gameapp or appstore folder (sorry I can’t remember what it was called) inside the FS2020 folder to Steam and restart the game. Then you only have to download the 8GB patch and NOT the whole game.
Hope this helps someone!