A new guide today in the Adafruit Learning System: Custom Controllers for MakeCode Arcade
You can now use a number of MakeCode-supported microcontrollers such as the Adafruit Circuit Playground Express, Adafruit Feather M0 Express and Adafruit Trinket M0 as custom arcade controllers in Microsoft MakeCode Arcade.
The Adafruit Circuit Playground Express has all kinds of sensors, buttons, and capacitive touch pads to make keypresses. But even the Adafruit Feather Express or Trinket M0 can be used in MakeCode Maker.
Tailor your needs to the boards available or have on hand.