Filter by custom field in custom post type on admin page

And for displaying result for Filter then try this code

add_filter( 'parse_query', 'prefix_parse_filter' );
function  prefix_parse_filter($query) {
   global $pagenow;
   $current_page = isset( $_GET['post_type'] ) ? $_GET['post_type'] : '';
   
   if ( is_admin() && 
     'competition' == $current_page &&
     'edit.php' == $pagenow && 
      isset( $_GET['competition-name'] ) && 
      $_GET['competition-name'] != '' ) {
   
    $competition_name                  = $_GET['competition-name'];
    $query->query_vars['meta_key']     = 'competition_name';
    $query->query_vars['meta_value']   = $competition_name;
    $query->query_vars['meta_compare'] = '=';
  }
}

Change the meta key and meta value as required.
I have taken “competition name as meta_key and “competition-name” as select drop down name.