For many, additional modifier keys means keyboard firmware changes with macro programming. My keyboard does not have media keys, but I have programmed the keyboard that Fn+Q sends the Volume Up key, Fn+A sends Volume down, Fn+W sends Play, etc. There is no Fn key in the HID specification (at least not that I'm aware of), the Fn key exists only on the keyboard's firmware.

Many keyboards these days are getting quite fancy. There's even an open source keyboard firmware standard. https://qmk.fm/