The app functions in much the same way as iTunes did for music, though it should be noted that the Apple Music integration, at least from a subjective viewpoint, seems much tighter. Here's how to use the Music app on macOS Catalina. The new Music app was supposed to provide a manual workaround, alas it didn’t. This seriously disrupts the DJ business on planet Earth — until Apple releases a fix in the next macOS Catalina update. The notable DJ apps affected by this are Traktor and Rekordbox.
To quit (close) a Mac app normally, choose Quit from the app's menu in the menu bar, or press Command (⌘)-Q. If the app doesn't quit, follow these steps to force the app to quit.
How to force an app to quit
Google Music App Macos Download
Press these three keys together: Option, Command, and Esc (Escape). Or choose Force Quit from the Apple menu in the upper-left corner of your screen. (This is similar to pressing Control-Alt-Delete on a PC.)
Then select the app in the Force Quit window and click Force Quit.
You can even force the Finder to quit, if it stops responding: Select Finder in the Force Quit window, then click Relaunch.
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How to force an app to close on your iPhone, iPad, or iPod touch.