Keys Function

I prefer the top row of keys to always behave as standard function keys without holding the Fn key and I did the following instructions :

Choose System Preferences from the Apple menu.

From the View menu, choose Keyboard.

Click the Keyboard tab if it is not already selected

Enable "Use all F1, F2, etc. keys as standard function keys."

but nothing changes I still can not use the keys for their special features printed on them neither with nor without holding Fn key

Thank you