Open functions.php in wordpress theme directory folder inside wp-content->themes->theme name folder then copy and paste the code below inside functions.php

add_action( 'woocommerce_product_query', 'whc_product_hide', 9999, 2 ); 

function whc_product_hide( $woo, $query ) {   
    if ( is_admin() ) return;   
      $meta_query = $woo->get('meta_query');   
      $meta_query[] = array(
         'key' => '_regular_price', 
         'value' => 0,
         'compare' => '>',
       );
   $woo->set( 'meta_query', $meta_query ); 
}

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