Custom 404 page not working I'm trying to set a custom 404 page but is not working.
What I tried:

configuration - system - basic site settings and set node path on 404 page -&gt; didn't work
add page--404.html.twig to my custom theme -&gt; didn't work
in my custom-theme.theme added _theme_suggestions_page_alter function -&gt; didn't work

Always show default 404 page, not my custom page.
I clear cache on every attempt.
Is there something I am missing?
Thanks in advance

Edited
Tried on local and cloud acquia server
I check with another websites that I build and all of them give me this 404 page (default)

But with this specific website I get this 404 page

It seems this website 404 error is handle by browser and not by drupal 8(?)

Edited 2
Another thing I notice is when I type a wrong URL appear on &quot;log messages&quot;

But on current website (the one I can't set custom 404) I don't have any error on &quot;log messages&quot;.
Is there any code/config to enable/disable this?
Maybe this is same problem?
Are your sure you did all the steps? Step 1: in mytheme.theme
/**
 * Implements hook_theme_suggestions_HOOK_alter().
 */
function MYTHEME_theme_suggestions_page_alter(array &amp;$suggestions, array $variables) {

  $route_name = \Drupal::routeMatch()-&gt;getRouteName();
  switch ($route_name) {
    case 'system.401':
      // Unauthorized Access.
      $error = 401;
      break;

    case 'system.403':
      // Access Denied.
      $error = 403;
      break;

    case 'system.404':
      // Page Not Found.
      $error = 404;
      break;
  }
  if (isset($error)) {
    $suggestions[] = 'page__' . $error;
  }
}

Step 2: create the page--404.html.twig file
Step 3: clear cache
For some markup, check https://stefvanlooveren.me/blog/styling-404-error-pages-drupal-8