I upgraded my OS to Catalina 10.15.6. and App Store became unresponsive after the installation. I did the following to try and fix the problem:
Made sure that the Apple IDs that were logged was consistent
Authorised the MacBook
MacBook Air 13″, macOS 10.15
Download and install this Update Combo over your current installation of macOS Catalina. It may be able to repair any problem with your current installation. It will not harm your Mac.
https://support.apple.com/kb/DL2048
ASC - Late 2012 Mac mini, macOS 10.14.6; Watch, series 5 GPS/cellular, watchOS 6.2; iPad Air 2, ipadOS 13.5.1; iPhone 8+, iOS 13.5.1; TV 4th Gen, tvOS 13.4.6; HomePods, audioOS 13.4.6 and Airport Express w/ Airplay 2
Download and install this Update Combo over your current installation of macOS Catalina. It may be able to repair any problem with your current installation. It will not harm your Mac.
https://support.apple.com/kb/DL2048
ASC - Late 2012 Mac mini, macOS 10.14.6; Watch, series 5 GPS/cellular, watchOS 6.2; iPad Air 2, ipadOS 13.5.1; iPhone 8+, iOS 13.5.1; TV 4th Gen, tvOS 13.4.6; HomePods, audioOS 13.4.6 and Airport Express w/ Airplay 2
App Store unresponsive after installing Catalina 10.15.6
