2 layers21.6 × 52.3 mm

Ps2 pico hat
No0ne/ps2x2pico
USB keyboard/mouse to PS/2 interface converter using a Raspberry Pi Pico
17 parts399MIT
KiCad boards from 2 GitHub repositories tagged “usb-keyboard”, the most starred first; open any of them in PCBKit.

No0ne/ps2x2pico
USB keyboard/mouse to PS/2 interface converter using a Raspberry Pi Pico

sam-was-here/PUMBA-Keyboard
PUMBA-Keyboard is a PS2 to USB macro board adapter