I want to share the working code here

Notes: this example code is copied from here, and it's target to M5Stack instead of M5Atom, so the default RECV PIN is 36, but for the M5Atom, you should use 32 as the default RECV PIN, the default means connecting IR unit via the HY2.0-4P cable.

#include <M5Stack.h>

int ir_recv_pin = 32; 
int ir_send_pin = 26;

int last_recv_value = 0;
int cur_recv_value  = 0;

void setup() {
  M5.begin();
  M5.Power.begin();
  pinMode(ir_recv_pin, INPUT);
  pinMode(ir_send_pin, OUTPUT);
  digitalWrite(ir_send_pin, 1);
}

void loop() {
  cur_recv_value = digitalRead(ir_recv_pin);
  if (last_recv_value != cur_recv_value) {
      if (cur_recv_value == 0) {  // 0: detected 1: not detected
          Serial.println("detected");
      }
      last_recv_value = cur_recv_value;
  }
  Serial.println(cur_recv_value);
}