How can I control Music with arbitrary global hotkeys (SizzlingKeys replacement) on Catalina?
Global hotkeys controlling Music even when in the background can be achieved by using a combination of MacMediaForwarder and Karabiner-Elements:

Install MacMediaKeyForwarder: https://github.com/milgra/macmediakeyforwarder/releases
Install Karabiner-Elements: https://karabiner-elements.pqrs.org
Configure Karabiner-Elements using &quot;Simple modifications&quot; so that your desired global hotkey maps onto key_code::play_or_pause (or any other action).

This can also be used to map the global volume control to arbitrary global hotkeys which I find very useful when using an external keyboard. (This does not require MacMediaKeyForwarder.)