How can i display tokens with html tags?
Try this one - 

$replacements[$original] = \Drupal\Core\Render\Markup::create("&lt;b&gt;Hello&lt;/b&gt;");


Helpful links:

https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Render%21Markup.php/class/Markup/8.2.x

http://www.drupaldump.com/drupal-8-how-have-custom-tokens-html-them-properly-replaced