I tried creating 2 key combination in Dispaly fusion.
One would just press "f8"
The other would just press "f"
Display fusion gave a warning that these keys are taken (duh), and it can remove them to allow display fusion to use them. I mistakenly said "yes", and now those two keys are no longer recognized by Windows.

I assume Display fusion did something with the windows registry?
How can I ix this? I need these keys back.

And if your wondering how I am typing "f" now its becuase I am literally copying and pasting an "f" from my clipboard...

I figured it out!
1. Go to Dispaly Fusion settings
2. Select "Functions"
3. Remove the custom keys I added.

Windows restores use of those keys after they are removed.