Thanks for your thoughts. I agree that using software would be easier, but I wanted to do it in hardware in this specific case.

I am unfamiliar with Raspberry pi, but if my understanding is correct, it's running a real os. So I would need to send it a command to actually shut down every time I want to remove the usb device. More generally, having a general purpose OS on the little device seems overkill for that use case, no?

I'm confused, why do you want hardware and what do you want the hardware to do? And, why not use a USB keyboard?

You could use an rpi pico. It has a usb port and there is a software hack to bit bang a second usb port, iirc.

I am wondering if connecting over USB is an XY problem.

To try and clarify a bit: I am essentially trying to have a KM (KVM without the V) over USB.

To go one step higher, I am trying to control a mac mini from the keyboard of a macBook.

Why not use the macs’ built in “sharing” functionality?

It usually runs a Debian based image. And you would probably just have to reboot the script, or write a wrapper around the keyboard functions.

But yes, it's overkill for an overkill solution. Buying another keyboard may be easier.