Fill Short Cut (Shift/F5) is not active when using Logi MX Keys keyboard

First thing I'd test is to see if any F-key shortcuts work that don't have modifiers. Like try adding just a shortcut for the action to "F5" and see. If it works like that it could be a clue.

I'd also check if shortcuts F5 or Shift+F5 in other apps. If not it's possible the keyboard has some kind of feature that locks the function keys to instead use the 'secondary' function like setting brightness or whatever else the F-keys have as dual purpose. 

Apparently there are "keyboard tester" sites like this one which can show you which keys are getting pressed, so maybe you can see if the keys you expect are actually registering: https://keyboardchecker.com/

(Just realized this is an old post so hopefully you figured it out before my response 💀)