Open The App Store On Your Mac. Open the keychain access app (applications > utilities > keychain access). With the app store window open in the foreground, tap the apple icon on the menu bar, and select 'force quit' or 'force quit app store.' that will launch the 'force quit applications' menu. To download apps from the mac app store, you need a mac with os x 10.6.6 or later.
You can just download whatever you need from the app store. Mac app store blank screen and other issues on macos catalina.
Mac app store and identified developers:
Open the app store and go to store > sign out.; Gatekeeper is the os x’s security feature that manages this kind of stuff for you. Launch itunes and select the pulldown menu located at the top left corner. If you purchased the application for mac under that apple id, you should see it in this list.
