Using Automator, I made a service that launches calculator.app. In System Preferences > Keyboard, I created the keyboard shortcut CTRL-OPTION-COMMAND-C to trigger the service. This works great except when Finder is in focus.
The service does work through the Finder menu bar: Finder > Services > openCalculator (the name of my service). But my keyboard shortcut appears to do nothing in Finder.
If I change the keyboard shortcut to some other combination, it works.
I looked through Apple's list of Finder keyboard shortcuts to see if CTRL-OPTION-COMMAND-C was mapped to something else but it wasn't in the list.
I am using Mojave.