App Store not opening after the latest Catalina update on MacBook pro

I had the exact same problem and found an answer that worked for me here:

https://www.reddit.com/r/MacOS/comments/enmnk6/app_store_completely_not_working_for_macos/

I opened up the Keychain Access app, then Preferences, then Reset My Default Keychains.

As soon as I did this it immediately worked, don't understand why or why this isn't anywhere on the Apple support forums. The suggestions on these support forums seem to be more about getting "points" than actually solving problems.

Boot into Safe Mode (Use Safe Mode to isoloate issues with your Mac) and try accessing the App Store from there. Reboot normally and try again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing some system cache cleaning, volume verifying and directory repairing. 

You shouldn't hijack this topic. Create your own topic after reading the following user tip and restate your question/problem in detail: Writing an Effective Apple Support Communities Question - Apple Community  

re-install the combo update on top of top of your existing macOS 10.15.2

Download macOS Catalina 10.15.2 Combo Update - Apple ...

I had the exact same problem and found an answer that worked for me here:

https://www.reddit.com/r/MacOS/comments/enmnk6/app_store_completely_not_working_for_macos/

I opened up the Keychain Access app, then Preferences, then Reset My Default Keychains.

As soon as I did this it immediately worked, don't understand why or why this isn't anywhere on the Apple support forums.

I opened up the Keychain Access app, then Preferences, then Reset My Default Keychains.

As soon as I did this it immediately worked, don't understand why or why this isn't anywhere on the Apple support forums.

Probably nobody who was having the same problem found the solution. It is now. Thanks for the feedback.

FWIW, this didn't work for me

Hi App Store is not responding on my mack Catalina 10.15.2

The MACOSupdCombo didn't work in my case. Any other recommendations?

I have the 10.15.3 update and having the same problem opening the app store. Any suggestions?

Having the same issue but I have update 10.15.3 so your link is not useful. Any other suggestions?

I found that creating a new user account in your MAC is a work around. I have not heard anyone address the issue from Apple.

Please. I need help. my app store not opening after the latest Catalina installation on MacBook Pro. Thank you

Finally! This just worked like a charm! Thank you so much.