How to: Option+F8 as a shortcut? (F keys)

Peter I am a little unclear on the process. I wanted to use Fn + K for a macro so from what you are explaining I can’t do that. So I hit “K” and then clicked on the “K” under ‘this hotkey’ and chose
Fn + Control + K. It does give me the result ’ ^k ’ so are my only options to use Control, Option, or Command and any combination of those key choices? My quest is to seek out combinations which are global and guaranteed not to be used in any program.

Also speaking of combinations which aren’t used in any other programs is there some place current program keyboard shortcuts that are currently active on my system can be listed using a utility or grep AND also highlight conflicts?