Wrapped up my documentation on this unusual mashup! https://flatfootfox.com/typeboy-keyboard-typepak-cartridge/
I managed to fit a XIAO BLE, Sharp Memory Display, shift register, and LiPo battery inside of a Game Boy Advance cartridge. The "TypePak" is mostly just for aesthetics, but it will make swapping microcontrollers more straightforward if I use it on future builds. The keyboard itself is pretty strait-laced 58 key split ergo outside of its GBA-compatible cartridge slot. I did some experimenting swapping out volume rotary encoders for thumb switches to try and keep the Game Boy vibes going. Everything's topped off with a few FK Custom keycaps.
This is really impressive. Great write up also, was cool to read through your process. One question though - what filament is that? I have been looking at those FK custom keycard, but the matching case really takes it to the next level.