On Mac OS, how do I move an app to another Desktop with a keyboard shortcut?

Another method (if you are asking about moving a window from one desktop to another): you can change desktops via control-# where # is the desktop number. If you grab a window by its title bar (as if to drag it somewhere) and then press control-6, say, the window will be moved to Desktop 6.

Also, you can assign all windows for a particular application to a particular desktop by using control-click on Dock icon, then "Options".

Mission Control in System Preferences and F3 on keyboard. After F3 pressed at very very Top of Screen Desktop appears. Move over it and far right + ( plus sign ) to add another Desktop. Add the desired Application in Desktop 2 that was just added.