How do i hide categories from menus which don’t yet contain posts?

Question

It depends which function you are using for querying those categories, but all of them has hide_empty argument

for example for:

<?php
     get_terms( $taxonomies, $args );
     $taxonomies = array( 
        'post_tag',
        'my_tax',
     );
     $args = array(
         'hide_empty'    => true, 
     ); 
?>

get_terms

by default, hide_empty argument is empty so check if it’s false in you code.