It says something that we have to be reminded of those old school debugging techniques that used to be part of our every day repertoire. MacOS has become VERY stable.
Originally Posted By: artie505
On the other hand, doesn't it seem bizarre that built-in key functionality is susceptible to a corrupted plist?

Keyboard actions are not hard-wired or at least what their effect is is not hard-wired. When you press a any key that action sends a code corresponding to the the position of the key on the keyboard to the host computer or device. That code is an index into a software table that determines what that particular key is and what should happen when it is activated. In Catalina System Preferences > Keyboard > Input Sources there are fourteen different keyboard layouts for the English language alone much less all the other language keyboards. Once you get into Shortcuts the sky is pretty much the limit. While the non-character keys do have a particular function by convention they are still interpreted in the same software table and they can be reassigned to do something entirely different.

OUT OF CURIOSITY You said you did not have com.apple.keyboard.plist or com.apple.keyboardservicesd.plist, do you remember what plists you ended up deleting?

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein