PS2 is a old PC keyboard (and mouse) connector/protocol used prior to USB. It is still available on some PC mother board. The protocol is serial and run at 5V, so it require electronic if your microprocessor is 3V.
Support for CircuitPython was added by user elvis-epx with the PR: adafruit/circuitpython#1893
The process to add PS2 protocol to CircuitPython was documented by the author: https://epxx.co/artigos/howto.html
Here is the CircuitPython documentation: https://docs.circuitpython.org/en/latest/shared-bindings/ps2io/index.html
You need to use a board that as the ps2io module build in, so check the support matrix: https://docs.circuitpython.org/en/latest/shared-bindings/support_matrix.html?filter=ps2io#module-support-matrix
https://docs.circuitpython.org/en/latest/shared-bindings/ps2io/index.html
Todbot sample code on how to use it: https://gist.github.com/todbot/08fbfc7613de6b3151f441ffa7f86584
Voilà
This board would be interesting to investigate, to connect a PS2 to a QT Py: http://land-boards.com/blwiki/index.php?title=TinyPS2
TODO: Take the KMK module for PS2: https://github.com/elvis-epx/kmk_firmware/blob/ps2_howto/kmk/ps2protocol.py Adapt it to the official accepted CircuitPython API. Propose as a PR to the main KMK repo: https://github.com/KMKfw/kmk_firmware And I think this should be used: https://github.com/elvis-epx/kmk_firmware/blob/ps2_howto/user_keymaps/epx/ps2converter.py