TL:DR make sure premium addon not linked to xbox live pass Steam Ver maynot link to it
and maybe check with steam before purchase if normal does not recognize will they provide DLC you may need to pay $ difference. Note your user progress also may not transfer, even with same xbox/msfs2020 ID.
I did that msstore to steam because of the way ms-store ver likes to load to Winapps protected folders.
I had premium addon from msstore and bought steam normal, Premium addons were not recognized by msfs2020 when i logged on.
Msstore addon premium package was available in game but only at FULL price ie normal + premium version costs. It may have been because i had originally had the xbox live pass, bought Full $price deluxe-premium version from store without uninstalling xbox pass, so it only would link to xbox pass version and not steam.
Luckily steam allowed me to change my normal versions and added DLC
but was very early on when MSFS first released, may not do that now, had to pay difference to upgrade.
I am happy i have changed to steam (90% of my games are steam}, as I use Mod and Vortex so don’t constantly get permission errors from ms-store version even though I have ADMIN access. Had to buy twice but I am in for longhaul and msfs forums are full of issues with ms-store version downloads etc…
I have had no issues with steam updates, but msfs2020 well happy to be a Beta tester lol