I wanted to keep Bluetooth off but still use a Magic Keyboard (USB-C) with my new Mac Mini M4. Here's how I succeeded.
When you have the Magic Keyboard connected via its cable, and you try to turn off Bluetooth, Mac OS will tell you you can't turn off Bluetooth because that would leave you unable to control the computer. This stumped me. Eventually, though, I plugged in a regular USB keyboard at the same time and then MacOS allowed me to turn off Bluetooth.
Voila! The Magic Keyboard continued to work, even after I unplugged the other keyboard. Reboot and the MK continued to work and when I checked System Settings, Bluetooth was still off.
Of course I also had a USB mouse connected through all this.
When you have the Magic Keyboard connected via its cable, and you try to turn off Bluetooth, Mac OS will tell you you can't turn off Bluetooth because that would leave you unable to control the computer. This stumped me. Eventually, though, I plugged in a regular USB keyboard at the same time and then MacOS allowed me to turn off Bluetooth.
Voila! The Magic Keyboard continued to work, even after I unplugged the other keyboard. Reboot and the MK continued to work and when I checked System Settings, Bluetooth was still off.
Of course I also had a USB mouse connected through all this.