Hi there,
I had the same problem, after restarting my Mac my Keyboard was firstly acting weird.
After playing around with the settings of the MX Keys and trying out a little, I ended up pressing the "fn key" right below the 1,2,3 button. Suddenly nothing really worked anymore, bottons 2 & 3 were triggering display brightness and other weird stuff.
Eventually I wen into my settings and removed the MX keys, trying to fix it by "just reconnecting it".
Doing so I ended up not seeing the device anymore at all – It seemed like my keyboard did not exist anymore and also the press and hold of the "1" button did not trigger a reconnection of the keyboard anymore.
Long story short, here is what somehow helped me and don't ask how I got there or which of the steps could also be left out:
- Reset the Bluetooth Module on Mac (holding shift + option and clicking on the bluetooth icon in the top bar > Debug > Reset the bluetooth module)
- Restart your computer
- Open Bluetooth Settings to search for devices
- IMPORTANT: As I was trying to reconnect my keyboard by pressing + holding the "1" button, still did not work or make the keyboard disappear: I had to hit the "fn" button right below it and then the "1" button and press + hold it for 3 seconds. (only this made the LED blink rapidly and eventually the keyboard appeared back as a new bluetooth device)
- Follow the general steps & do not use the num pad on the right to enter the connection code
Hope this is helpful to someone else who's playing around too much in the settings
I think the issue here is, that there is somewhat of a "fn-lock-mode" which is not visible through any LED or software element.
Hence, nobody realises it is actually active and preventing certain buttons to work the way they should.
