I regularly switch between a modern PC and an ancient one which only supports PS/2. In order to use my USB mouse and keyboard, I use ps2x2pico: https://github.com/No0ne/ps2x2pico
Since both projects use the pico, I figure it wouldn't be hard to integrate its codebase into yours in order to make PS/2 a possibility on one or both sides.
I regularly switch between a modern PC and an ancient one which only supports PS/2. In order to use my USB mouse and keyboard, I use ps2x2pico: https://github.com/No0ne/ps2x2pico
Since both projects use the pico, I figure it wouldn't be hard to integrate its codebase into yours in order to make PS/2 a possibility on one or both sides.