I have a Lenovo m90q which has a smart power on USB port. You can plug a keyboard that supports this in this port and when you press Alt+P on the keyboard, the computer will power on. I have checked that this works with a regular keyboard, and it did. After that, I wanted to make this happen with a Raspberry Pi Pico. So, I adapted a TinyUSB composite HID example to only include a keyboard and press Alt+P when a GPIO pin was pulled down. The code is quite long, so the full code can be found at GitHub. I am using the Pico C/C++ SDK to build this.