Sorry for the late reply but your post was waiting to be approved so didn't show up as a latest post.
I'm unsure as to which repair WR said it couldn't fix for 20H2 - can you post your repair log.
There is an option to access those from the main UI of WR.
I've just ran the full repairs on this 20H2 and other than the Win 8/10 App repair which is skipped, all report as being done.
I've come across this article which may resolve your App Store problem -
https://www.makeuseof.com/tag/5-tips-fix-windows-store-app-issues-windows-10/As an alternative to a clean install, in the advanced boot options there's an option to Reset where you can retain your personal files but it will remove all 3rd party programs, so you would need to reinstall those.