MSFS 2020 Stuck on "Press any key to start" - A special character user will cause a problem!
I completed the full troubleshooting guide put out by Microsoft, and my problem was not solved. Luckily I saw buried in an unrelated thread that sometimes usernames with special characters can cause a problem. In my case, Windows 10 added a special character into my user account when I installed 10 for the first time, it had never caused problems until MSFS 2020.
The solution is to make another user account (make this a local user with admin priv) with all normal letters, then copy over the files you need essentially, migrating you entire user account to this one with a better name. Once you get a good windows 10 profile, with no special characters, you can boot up Microsoft store, log in with you account, and download the installer with no issues.