Action on Middle-Click on Desktop For years, when I used X, I had it configured so that a middle-click on the background would instantly create an xterm right there.  Apparently, old habits die hard, as I just tried to middle-click myself a Terminal.app window, despite not having used X regularly in nearly 20 years.
So, is it possible to configure an action to start an app/open a new window in an app on middle-click on the desktop?
As Apple has never sold a mouse with a middle button, macOS has never had native support for assigning any custom actions to that input.
However, there are a variety of third-party utilities which will enable this, such as BetterTouchTool or Multitouch.