How can I use F6 to convert into hiragana in Japanese keyboard? I just found a way to convert into hiragana on Japanese keyboard using F6, but the F6 key is used to change the illumination of the keyboard in default.

But since my MacBook does not have any illumination, it is of no use, and rather want to use it as a conversion on the Japanese keyboard.

Is it possible to enable it, withouth keyboard hacking software like Karabiner? Or is it only on some specific models of Macs? I use High Sierra on 2017 MacBook.
You can enable Use F1, F2, etc. keys as standard function keys under System Preferences app → Keyboard → Keyboard, as shown: