posts_per_page_tribe_category.php

<?php
add_filter( 'pre_get_posts', 'expand_tribe_category_ppp' );
function expand_tribe_category_ppp( $query ) {

  if( is_admin() ) 
    return $query;
    
  if( $query->tribe_is_event_query() && is_tax( 'tribe_events_cat' ) ) {
    $query->set( 'posts_per_page', 10 );
  }

  return $query;
  
}