Wait, the sim wanting to reinstall is a common issue with the MS Store version of the sim.
The base issue is that somehow the XBox app either didn't identify you correctly, or it forgot where your sim was installed.
If you point the installer to your actual installation folder, it will recognize the files are already there and won't download a thing.
So, whenever something like that happens, if you reach the "update/install" screen where it tells you it needs to install more than 100 GB of data, do the following:
1- kill the sim
2- go to the XBox app
3- force a logoff of your user, and log on again
4- relaunch the sim
5- if it *still* wants to redownload everything, edit the install path to match the one you had chosen upon your original installation of the sim
6- the sim should find your files and proceed with the loading to the menu.
Now don't get me wrong, I fully agree the problems of the MS-Store version of MSFS regarding lost installations, erased addons and lost settings are unacceptable, and Asobo should fix that ridiculous nonsense. But in 4 years, they couldn't fix that, so I'm not too optimistic about seeing these problems solved any time soon. Same will happen with MSFS2024 I'm sure.