woocommerce_is_sold_individually.php

<?php
/**
 * Remove quantity field from single product pages for specific products
 * Update list of product IDs
 */
function pr_is_sold_individually_product_list( $individually, $product ) {
   if( in_array( $product->getid(), array( 1234, 5678 ) ) ) { // Update the IDs in this list
      $individually = true;
   }
   return $individually;
}
add_filter( 'woocommerce_is_sold_individually', 'pr_is_sold_individually_product_list', 10, 2 );