GitHub - Ladus/ArduinoKeyboardFirmware: Arduino keyboard firmware to convert a key matrix into keyboard input with multiple switchable key layers. Initially made only for the Pro Micro, but may be extended towards other
Overview | Using QMK on RP2040 Microcontrollers | Adafruit Learning System
I once used Arduino Uno as a HID, and I can't turn it back to normal Arduino. - Installation & Troubleshooting - Arduino Forum