A couple thoughts…

I’ve used both USB to PS/2 converters, and “modern” PS/2 keyboards on retro machines. For what it’s worth, I’ve had a lot of success with this particular model of PS/2 keyboard: Perixx Keyboard

As for USB to PS/2, a traditional adapter like this has worked for me previously for generic USB keyboards (think Amazon basics kind of stuff). I’ve never tried a more full-featured USB keyboard on a retro PC, so I’d imagine that could be tricky (or may even be totally unsupported).