Well, now i need to recheck what i have been doing.
Your example works both on M5Stick (using ports 0 and 26) and M5Atom (ports 26 and 32).

Thank you, i have some work to do, Ha Ha

have you tried directly looping back TX into RX? E.g. connect G26 to G32? Then try withsomething like this in the loop():

  static uint32_t lastTime = 0;
  if(millis() - lastTime > 5000)
  {
    lastTime = millis();
    Serial1.println("hello");
  }
  if(Serial1.available() > 0)
  {
    while(Serial1.available() > 0)
    {
      Serial.print(Serial1.readStringUntil('\n'));
    }
    Serial.println();
  }

Thanks
Felix