App Store Broken [duplicate]

Solution 1:

The CSS needed to render the old App Store is not being served. That explains only the visual change, not the lack of function.

You may need to update the OS or use a command line tool like mas if you can’t operate the controls without the web app rendering properly.

• App store update page doesn't seem to be loading properly on Mac OS El Capitan 10.11.6
• App Store Updates does not renders correctly in High Sierra

For security updates, you should be able to run softwareupdate -aiR from terminal and avoid the app needing to function at all. Should that fail a backup and restore or deeper triage is needed to isolate what’s causing the failure to operate in that app.