I believe there is an error on the "Tech Specs" link of the Arduino Micro, namely on these two websites:
https://store.arduino.cc/arduino-micro
https://store.arduino.cc/arduino-micro-without-headers

Specifically, the indication "DC Current per I/O Pin | 20 mA" is not correct: it should be 40mA. This information can be found on the datasheet of ATmega32U4, Section 29.1, page 383.
Interestingly, the same information appears correctly indicated on the "Tech Specs" of the Arduino Leonardo, which uses the same chipset as the Arduino Micro:
https://store.arduino.cc/leonardo