Some other options to convert USB to PS/2 if you are willing to build it yourself:
- GitHub - rasteri/HIDman: Adapting USB devices to work on old computers
- GitHub - No0ne/ps2pico: USB keyboard to PS/2 / AT / XT interface converter using a Raspberry Pi Pico and ps2x2pico
I’ve been intending to build some of the ps2pico ones for myself and I could build some extra if people are interested.