Most Efficient Way of Combining Large Strings for HTML Response

Projects Programming
8

Nope, no joking. It was pseudo code to convey a concept of what I'm looking for and asking the experts to fix it. Are you able to fix it?

Here, I'll simplify it more and made sure it compiles.

void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
  String test = returnHTML();
  Serial.println(test);
  delay(500);
}
  
String returnHTML()
{
     String strHTML = "";     
     int j = 0;
      
     while (j < 20) {
        strHTML += "This is a test.\n";
        j++;
      }
      return strHTML;
}

jremington:
Surely you are joking.

You offer function code that (if it worked at all) would create a String that contains about 20x20000 characters on an Arduino, when you have been advised not to use Strings at all?