App Store hangs after Catalina (10.15.7) reinstall

I just reinstalled the latest Mac OS version of Catalina on my old mac book (mid 2012) and my App Store app is not opening properly. When I open it the screen opens up and the beach ball keeps spinning for more than an hour. I have to force quit because 'application not responding'. I have tried everything and nothing seems to fix it. I've tried to change the date and time, and tried rebooting, and reinstalling the OS with no success. Does anyone know how to get the App Store app working again?

Thanks,

Mike