The volume customer keys of my Mac don't work anymore
Basically
- Open System Preferences
- Select "Keyboard"
- De-select "Use F1, F2, etc., keys as standard function keys"
My volume-key issue occurred suddenly so it probably was not due to messing up settings manually. I detached my bluetooth keyboard and then reconnected it. The volume keys started working again.
This may not solve everyone's problem but it doesn't hurt to try if you see similar things.