I have the downloadversion from MS Store of MSFS2020 Standard.
Since a few days i was getting the 'insert disc' error.
I noticed that the Digital Ownership Package from MS Store could not be downloaded at all.
After a lot of trying and testing i found out that apparently an upgrade of my Antivirus Software Bitdefender was causing the problem.
A few days ago i was upgrading from Bitdefender 2020 to the new Bitdefender 2021 Version.
While MS FLightsime ran wonderfully with Bitdefender 2020, it is not the case wiht the new Bitdefender 2021.
I deactivated Bitdefender 2021 and i could start MSFS2020 just fine.
No more 'insert disc'
Just opened a ticket with Bitdefender support on how to get MSFS2020 running with Bitdefender enabled...