Hello, youssefibrahim1.
I understand that, since updating, you have been unable to access the App Store. I’m glad you took the time to post and happy to help out.
The first thing I would check is to see if the App Store is all systems go via Apple's System Status. If everything is looking good, I would go ahead and restart your Mac.
Log out, sleep, restart, or shut down your Mac
If, after a restart, the issue persists, I would like to know if you can access the App Store while in a test user.
How to test an issue in another user account on your Mac
If the issue is present in your original user but not in a test user, the next step would be to reset the keychain. I should note in advance that resetting your default keychain, " deletes all the passwords saved in the keychain."
To reset the keychain:
1. In the Keychain Access app on your Mac, choose Keychain Access > Preferences.
2. Click Reset My Default Keychain.
3. In the Finder on your Mac, choose Apple menu > Log Out. When you log in again, save your current login password in a keychain.
I would also take a look at the support article, If you can't connect to the App Store, iTunes Store, or other Apple services. Step 4 is the key callout here.
Make sure that the date and time on your device are set correctly for your time zone.
On your iPhone, iPad, iPod touch: Open the Settings app. Tap General, then tap Date & Time. Get more help with date and time.
On your Mac: Open System Preferences, then choose Date & Time.
On your Apple TV: Go to Settings > General > Date and Time.
If the date and time are incorrect, update them or turn on the option to set date and time automatically.
I hope this helps!
Best Regards.