Is the game going to be written in MakeCode Arcade? Something else?
What you may want is to use the micro:bit as a Bluetooth joystick. Have you seen this Anyone ever used microbit as a controller? - #4 by Purp13 and this https://support.microbit.org/support/solutions/articles/19000071689-can-i-control-my-pc-or-simulate-a-keyboard-and-mouse-