Concatenate url() in Twig
The url function returns a render array, so you can't concatenate it with a string.  You must first convert it to a string.

try render_var():

{% set support_url = render_var(url('&lt;front&gt;')) ~ 'support' %}

&lt;h1&gt;{{ support_url }}&lt;/h1&gt;


This will convert the render array created by the url function to a string.