Q: Mac App Store does not open

I don't know of a case like yours in which the steps I've suggested so far failed to resolve the problem. Please delete the following item, if it exists, then log out and test:

~/Library/Containers/com.apple.appstore.PluginXPCService

If you missed any of the items I mentioned earlier, this is going to get very complicated, and the problem may not be solved.

Back up all data.

Hold down the option key and select

Go ▹ Library

from the Finder menu bar. From the Library folder, move the entire contents of the subfolder "Caches" (not the folder itself) to the Trash, then log out and log back in. Empty the Trash. Test.

If the problem is not solved, open the Library folder again in the same way and move the entire contents of the subfolder "Preferences" (not the folder itself) to a new folder on the Desktop (not to the Trash.) Log out and log back in. The account will then be pretty much in a clean state. Test. If you can still reproduce the problem, then put the Preferences folder contents back, replacing any that were created in their place, log out, and log in again.

If you can't reproduce the problem in the clean state, then start putting things back in the Preferences folder piecemeal, starting with items that seem unrelated to the issue. I can’t be more specific. After each group of items, repeat the log out/log in cycle and test. At some point, the problem may reappear, in which case you know that something in the last batch of files you restored is at fault. If it never reappears, the problem is solved.