How do I restore the behavior of the fn key after Mojave update?
Soooo . . . I've done this to myself.  I'm not sure how I've done it, and I don't like answering my own questions, but in case anybody else finds themselves in this situation . . . here goes.

I never use caps lock so I typically remap caps lock to control.  While I was doing this, evidently, I also remapped fn to escape by accident.


Apple > System Preference > Keyboard
Click 'Modifier Keys'
Sometimes there's a dropdown allowing you to remap the fn key (it seems like it's only there when you have an external keyboard too which may be why I couldn't find it when I looked here before to reset the behavior)