SoftwareSerial Nano Every minimum baud rate

Those text labels for the pins on the Nano Every board are so small ! :mag:

I did a test with a Arduino Every.
Connected TX1 to RX0, and run this sketch:

// Test Serial1 Arduino Every
//
// Board: Arduino Every, with TX1 connected to RX0.
// Arduino IDE 1.8.15

void setup()
{
  Serial.begin( 9600);             // to the computer
  Serial1.begin( 9600);            // looped TX1-RX0

  Serial.println( "Type something, and it will echo via Serial1");
}

void loop()
{
  if( Serial.available() > 0)      // something from the computer ?
  {
    int inChar = Serial.read();
    Serial1.write( (byte) inChar); // write it to Serial1
  }

  if( Serial1.available() > 0)     // something from the looped Serial1 ?
  {
    int inChar = Serial1.read();
    Serial.write( (byte) inChar);  // send it to the computer
  }
}

That works.

Your sketch is waiting in a while-loop, has a delay, and it reads reads two bytes, that is impossible to be reliable.
As you can see, my sketch is the cleanest way to echo the data. That works because it is so simple. Don't overthink it, follow the KISS rule.

By the way, the AltSoftSerial is not compatible with the Nano Every.