Trying to install fonts to Font Book (Mac) using the Terminal
/System/Library/Fonts is restricted with System Integrity Protection, since this folder is intended purely for macOS built-in first-party fonts.

Instead, choose one of the following locations depending on your intentions:


/Library/Fonts to apply to every user, existing and newly created.
~/Library/Fonts to apply to the current user.
/Library/User Template/Non_localized/Library/Fonts to apply to new users.