For machines with the Touch Bar, this can be achieved using System Preferences -> Keyboard -> Shortcuts and choosing "Function Keys" from the list of categories

For machines with the Touch Bar, this can be achieved using System Preferences -> Keyboard -> Shortcuts and choosing "Function Keys" from the list of categories. You can then specify apps that should show function keys instead of app controls by default. (i.e. inverts the behaviour of the fn key in the listed apps.)