It will take a considerable amount of time to download, even in the background and depending on your ISP download speed. Thus, you can delete the App Store cache on your Mac to bring it back to normal.The macOS Catalina Installer app is a 5 GB file.

When the apps run abnormally on your Mac such as Google Chrome keep crashing, clearing the app cache is a considerable trick to fix problematic apps. And the frozen App store may return to normal after restarting. It terminates all running programs and gives the Mac a fresh startup. Whenever the Mac is undergoing malfunctioned performance such as Mac stuck on checking for updates and Safari won't open, you can give it a shot. Restarting Mac seems like a good rule of thumb. Besides, you can sign out and sign in your Apple ID(Apple menu > System Preferences > Apple ID > Overview > Sign out) on Mac to troubleshoot App Store not working issue. Mac App Store will not allow you to update the app that is purchased with another Apple ID. If you have multiple Apple ID accounts, make sure you have signed in to the Mac App Store with the right one. Then, relaunch the App Store to see whether it works. If the App Store freezes, shows a black screen, or is stuck when updating/downloading apps, you can force quit the unresponsive App Store using the Apple menu, the Option + Command + ESC keys combination, Mac Dock, and Activity Monitor. Whether you encounter the 'Your clock is ahead' error when browsing websites on Mac or the MacBook shows the wrong date and time, you can find the solutions in this post. Why 'Your clock is ahead' on Mac & How to Fix?

Check from the Apple menu > System Preferences > Date & Time, and you can simply choose Set date and time automatically to avoid clock errors on Mac. Such incompatibility may cause the App Store can't download and update applications. In case the date and time are wrong on your computer, there is a discrepancy between your Mac and the Apple server. You can head to the system status page to check whether the Mac App Store is available now. If so, you may be unable to use the Apple store for a while until the Apple system resumes work. Perhaps, there is an outage of the Apple system. You can turn WiFi off and reconnect it, use an ethernet cable, or reset network settings. Therefore, if the App Store can't load on your Mac, perhaps, you haven't established a quality WiFi connection on the Mac. To update macOS and download apps in the App Store, it needs a stable internet connection to load the resource from Apple's servers. Switch to another account/create a user account.

Mac app store not downloading