Comment by Someone

> I want to build a little device that connects two computers together via usb, and send keystrokes from one to the other.

> (I would use it to use a laptop keyboard on a headless computers).

Are you sure you need such a device? If this is to occasionally manage that headless system, wouldn’t a Remote Desktop connection work fine?

You’re mentioning a Mac Mini and a MacBook elsewhere, so https://support.apple.com/en-gb/guide/remote-desktop/apdf49e... might be sufficient for your needs.