How to use f11 on a Mac
Solution 1:
System Preferences > Keyboard > Shortcuts > Locate "F11" and uncheck it for Show Desktop (or whatever its set as)
Solution 2:
Hit the Fn key at the bottom left along with F11. Alternatively, in System Preferences, you can set the F keys to be used as F keys and not as volume etc., so then you won't need to press the Fn key every time.
Solution 3:
On macOS 11 Big Sur you can find the option under:
System Preferences > Keyboard > Shortcuts > Mission Control
Then disable the F11 shortcut.
Solution 4:
I find this definition to be helpful towards the question:
The F11 function key will quickly slide up all your windows, revealing your desktop, and letting you interact with your files and folders. By default on MacBook / Pro / Air, and on the small keyboard for iMac, the F11 key is mapped to special functionality, like decreasing the volume. All you need to do is hold down the "fn" function key (bottom left corner of your keyboard) while pressing the F11 key to trigger the show-desktop command.
source: http://in5stepstutorials.com/mac-os-x/quickly-show-desktop-in-mac-os-x-gesture-hotkey.php