Use the "wordads_ads_txt" filter since Jetpack 6.1. See the official guide at https://developer.jetpack.com/hooks/wordads_ads_txt/

wordads_ads_txt.php

<?php 

add_filter( 'wordads_ads_txt', 'dat_wordads_ads_txt'); 
function dat_wordads_ads_txt ($ads_txt_transient) {
  $my_text = "#Add more texts";
  $my_text .= "\r\n"; // new line 	
  $my_text .= "google.com, pub-0000000000000000, DIRECT, f08c47fec0942fa0"; // Edit your own text here
  $my_text .= "\r\n \r\n"; // new line 
  return $my_text . $ads_txt_transient; 
}