Turn your ProMicro into a USB Keyboard/Mouse - SparkFun Electronics
Arduino USB HID Keyboard - MitchTech | MitchTech
AN #197 - Additional PC Multimedia USB-keyboard. - MCS Electronics
GitHub - houkanshan/arduino-bt-hid-proxy: Bluetooth HID proxy is implemented using Arduino. Make a Bluetooth keyboard or mouse (WIP) work in BIOS or device without BT stack (e.g. TMK USB to USB Converter)
USB multimedia keys on Arduino STM32 · One Transistor