Pro Micro pinout

The Arduino Pro Micro is cheap (~3$) and perfect for small boards (less than 81 keys). With a little hack though, it can drive a keyboard with up to 100 keys.

STeMCell - STM32 based pro micro pinout : r/ErgoMechKeyboards

Handwire Rotary Encoder to Lily58 Pro Guide - kriscables

Products

Pro Micro & Fio V3 Hookup Guide - SparkFun Learn

Arduino Leonardo Pro Micro Atmega32u4 5V 16MHz – Maker Zone

Arduino Pro Micro Atmega32u4 Board at Rs 390/piece, Arduino Electronic Development Board in New Delhi

Fixing an Arduino Pro Micro: the USB Port Came Off !! : 17 Steps - Instructables

Qwiic Pro Micro USB-C (ATmega32U4) Hookup Guide - SparkFun Learn

Arduino Pro Micro Board, 14 at Rs 370/piece in Thane

Pro Micro/type-c Usb 5v 16mhz Board Module For Arduino/leonardo Atmega32u4-mu Controller Pro-micro Replace Pro Mini - Integrated Circuits - AliExpress