为什么wp_title过滤器根本不起作用？

Question

I know there are other questions like this but didn't find a reliable answer. So:

First activate the thing (simplyfied code):

add_action( 'after_setup_theme', 'theme_setup' );
function theme_setup() {
  add_theme_support('title-tag');
}

Second, delete title tag from header.php.

Third, on page templates, before calling get_header(), add something like this:

  add_filter('wp_title', 'set_custom_title', 10, 3);
  function set_custom_title($title, $sep, $seplocation){
    return 'test';
  }

Well, this is not working at all, in any template, being a page, an archive, a custom taxonomy or post type archive. No nothing. Wordpress is generating titles by itself.

Why? Am I doing something wrong? Note that this code once upon a time just worked: used in other sites/themes.

Is it maybe an issue of wp5.2.0?

Answer 1

So, thanks to @Vel, the answer is to re-add the title tag (even if in previous wp versions > don't know til what version you had to delete it form head instead).

Current working code for me:

//functions.php
add_action( 'after_setup_theme', 'theme_setup' );
function theme_setup() {
  add_theme_support('title-tag');
}

//header.php
<title><?php wp_title('|', true, 'right'); ?> | <?php echo get_bloginfo('name') ?></title>

//page templates
$window_title = // do something
add_filter('wp_title', function($title, $sep, $seplocation) use($window_title){ return $window_title; }, 10, 3);