Black screen in Microsoft Flight Simulator Premium Deluxe Edition

let us first start with the easy stuff, because well known:

Dont press “Verify files” in Steam, otherwise all will be reininstalled. There is open issue for that

Then to the main problem:

to be sure: you installed MSFS the fist time ever , or is it a re-installation ?

You can may be try to remove files from AppData for a “fresh” start. Depends on where you have installed the Packages folder, you can remove the whole AppData\Microsoft_FlightSim… folder or not. If “Packages” was installed in Steam-Default location , then it sit within the AppData folder. Then you can remove all files/folders, except the Packages. Or you move the Packages folder to e.g. a D: drive and in next start of MSFS you set that Path in the “updater” ( so you not need to redownload ).
( e…g create a folder like D:\msfs , move Packages into so that you have D:\msfs\Packages )

Before you then Start MSFS again, ensure that you can login into the xbox app. Logout in xbox-app, Restart windows ( choose restart, not shutdown+start ) , Login into xbox app.
( note: gameing services are not needed for Steam users, so still optional also if that company MS will try to force you to install that buggy stuff ).

I also remember some rare cases, where the login dialog was in background. So try Alt+Tab and check whether a dialog is “waiting” while black screen is in front.