Had same problem here after changed motherboard and cpu.
Try all solution I could find.
I have a digital copy and no disk version
My solution: Uninstall msfs 2020 and digital ownership (I used IOBIT uninstaller) and rebooted.
In MS Store under library i found “Microsoft Flight Simulator Standard 40th Anniversary Edition” and “Digital Ownership” and chose “get från xbox” (hämta från Xbox-app in swedish) and it’s works again after 165 GB download.
If it happen again I think I will rename the “Microsoft Flight Simulator Digital Ownership” map and try to start the simulator and if that not work try to reinstall only Digital Ownership från MS Store.