How to display the On-Screen VOLUME indicator?

I would like to trigger the macOS's On Screen Volume indicator like the one that appears when you change the volume using MacBook Pro keyboard or Magic keyboard.

I would really appreciate any help on this matter.
Are you asking about creating an NSPanel similar to the one presented by the system, and if so, exactly what are you wanting to do?

How to display the On-Screen VOLUME indicator?
 
 
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