Hi SanDiegoImac
It is quite possible for the down-arrow key to mechanically fail on both your MacBook Pro and your iMac Pro.
Keyboards are basically mechanical devices and wear rates on individual keys depend not only stroke counts but also the complex relationship of individual human physiology, biodynamics and keyboard ergonomics.
The direction and force used to hit an individual key as well as the frequency of use will determine its life.
There are two methods you can use to determine if the keyboard is mechanically ok or whether software is to blame.
- Using the (virtual) Accessibility Keyboard (see following link).
https://support.apple.com/en-gb/guide/mac-help/mchlc74c1c9f/mac
Bring up the Mac Preferences page and under the Keyboard menu click on Input Sources then select Show Input menu in menu bar.
Close Preferences and click the keyboard icon that should now be visible on the desktop menu ribbon.
In the Keyboard menu drop-down click Show Keyboard Viewer, a graphic display of the Mac small-form keyboard will appear on the desktop.
As you click each physical key on the actual keyboard the corresponding key on the Keyboard Viewer will change its appearance.
If using dark-theme on the Mac then the outline of the active key on the Keyboard viewer will change shade/colour from grey to red.
The Keyboard Viewer also works as a virtual keyboard and allows you to type and navigate around open documents just the same as a physical keyboard and you can use this to verify that keyboard mapping in the OS has not changed.
Open a new or existing text document and enter new text or edit existing text by typing into the document using mouse clicks on the virtual keyboard, then navigate around the document using the arrow keys.
If the down-arrow key works from the virtual keyboard but not from your physical keyboard then the software side is ok and mechanically/electrically the keyboard is probably broken.
2 . To verify a suspect keyboard is really broken connect a different standard keyboard to your iMac or MacBook and test the direction keys using that, doesn't even need to be a Mac keyboard , a Microsoft Windows keyboard works just as well for testing the direction and standard QWERTY keys.
