I have a similar project inspired by another similar project (
https://github.com/jfedor2/screen-hopper).
My own version of this consists of two programs.
One program runs on a Linux desktop and listens to input events from the Linux input subsystem (evdev). When you press a specific key, it will start consuming all events and sending them over USB serial to a RPI Pico. Pressing the key again will toggle back into passive listening mode.
The RPI Pico is programmed to receive Linux evdev events over serial, translate them into USB HID events and send them to another Windows PC.
The end result is a KM switch that switches instantly between a Linux PC and a PC running an OS of your choice.
Epic wiring photo: https://ibb.co/m0zhzgz. I used another Pico as a USB serial adapter.
As a hardware noob, needing only 2 wires was a huge relief and I think this is a great starter project for other hardware noobs.
Both programs were Ultimately I never ended up open sourcing it because of some USB serial bugs (it would not reconnect properly to the Linux desktop after getting disconnected). Not sure if it was because of Linux or the Pico. I still use it, the bugs aren't a problem because I never disconnect the wires.
I also specifically left out the absolute mouse feature since I play a lot of FPS games and it wouldn't work with those. I have the switch key bound to a button on the side of my mouse anyway so I can switch systems without even touching my keyboard.