I have a 2020 MBP running Catalina. I have a Magic Keyboard with no Touch ID and a number pad and everything works fine. I also have a smaller Magic Keyboard (also no Touch ID) and no number pad and whenever I press the media keys it just sends the Fn key. My Touch Bar doesn't show the function keys unless I press Fn, and holding Fn on the keyboard makes them show up on the Touch Bar. I've tried two keyboards.
- Disconnect the Magic Keyboard with Num Pad
- Go to System Preferences > Keyboard
- Uncheck "Use F1, F2, etc. keys as standard function keys on external keyboards"
If this does not help, go to Bluetooth settings and remove both external keyboards. Pair the one without Numpad, repeat the steps above, then pair the Magic Keyboard with Numpad.