Q: Unable to open Mac App Store App

Not sure what you mean by bottom tray.   Have you tried Apple logo (top left) ... and click on App Store, 4th item down.

I think he is referring to the default position of the Dock, which is across the bottom of the screen.

Late 2012 Mac mini, macOS ?;  Watch, 38 mm silver AL, Watch OS 2.2.1; iPad Air 2 & iPhone 6+, iOS ?;  Apple Airport Express

Thanks Dah*veed.   Clearly you were correct.

Very interesting.  After you have approached it by Apple logo (top left) > App store, can you show us a screen shot of the 'ribbon'.   At that point you should be in the App Store.

The App Store in the iTunes App for Mac is a different App Store. The iTunes App Store is the app store for iOS devices; iPhones, iPads & iPods. Those apps will not run on a Mac. The Mac App Store normally available in the Dock & the  menu has apps for Macs.

I suggest restarting your Mac in Safe Mode. Restart your Mac and as soon as your hear the startup chime, press & hold the Shift key on the keyboard. You may release the key when the  logo and the startup progress bar appear in center screen. This startup method takes longer so be patient. In Safe Mode try to open the Mac App Store.

Just restart your Mac and don't press any keyboard keys to return to a regular startup.