Not sure.
I do know there have been a lot of complaints from people that had tried out the game pass version and bought all sorts of aircraft and scenery and even the Deluxe or Premium upgrade while on gamepass and then for some unknown reason bought the full version with a new MS login and new gamer tag and lost all their addons and upgrades they purchased.
Apparently MS support refuses to transfer anything over if you do that, once you buy something in the marketplace it permanently attaches to the gamer tag you were using when you purchased it.
In a way that is fair enough if you had two Steam accounts I doubt Steam would let you transfer games or DLC between them either.