I use LaunchBar to make me more productive. With LaunchBar, I can switch to another application by entering a few keystrokes, run a quick search with Google and so on. Before macOS Catalina and its new Music application, LaunchBar was also able to play and pause music in iTunes.

When you trigger iTunes - Play/Pause action via LaunchBar, you will encounter an error message like this.

An error occurred while running iTunes - Play/Pause

So how does the iTunes - Play/Pause work? Open the iTunes - Play/Pause action from Action Editor, you will see a script like this.

-- iTunes - Play Pause
-- LaunchBar Action
-- default.scpt
-- Version 5
--
-- Copyright (c) 2006-2016 Objective Development
-- https://obdev.at/

tell application id "com.apple.iTunes"
	if «class pPlS» is «constant ePlSkPSP» then
		«event hookPaus»
	else
		«event hookPlay»
	end if
end tell

Because macOS Catalina does not come with iTunes installed, the action (or AppleScript) fails to run.

You can replace tell application id "com.apple.iTunes" with tell application id "com.apple.Music" and save the script. Or you can also replace it with tell application "Music" as well. You can do the same for rest of the iTunes - … actions.

I’m not sure when LaunchBar will update its actions, but I suspect there are many people who are still running macOS Mojave or older. I have not figured out how to fix music library navigation issue yet. If you know how, please let me know.