FCP 10.4 - F10, F11, F12 not assignable???

I have use F1, F2, etc as function keys checked in system preferences, and I'm able to assign keyboard shortcuts to all F keys (F1 through F9), but not F10, F11, F12. Is this normal in FCPX? Shortcuts assigned to F10, F11, F12 don't work. Having assigned Show/Hide Timeline Index to F9, I was hoping to be able to assign View Clips, View Tags, View Roles to F10, F11, F12.

Is there something in Mac OS X High Sierra that prevents the volume keys F10, F11, F12 from being assigned in FCPX even when use F1, F2, etc as standard function keys is checked???