I was facing the same problems with String variable so I used to iterate and print each char at every index of the String. The text typing from Serial Monitor included in the code.
#include <TVout.h>
#include <fontALL.h>
TVout TV;
String text = "Please enter data in serial monitor";
void setup() {
Serial.begin(9600); // opens serial port, sets data rate to 9600 bps
TV.begin(NTSC,128,56);
TV.select_font(font6x8);
}
void loop() {
while(Serial.available()) {
text = Serial.readString();// read the incoming data as string
Serial.println(text); //open Serial Monitor to see what text You just printed.
}
for (int i = 0; i < text.length(); i++) {
TV.print(text.charAt(i));
}
TV.delay(1000); // wait 1 second
TV.clear_screen();
}