searchform.php doesn’t work properly

action="<?php esc_url( home_url( "https://wordpress.stackexchange.com/" ) ); ?>">

You forgot to echo out the URL, making the action attribute this:

action=""

This means the form is submitted to the current page, and since the current page is a category archive, it appends the s parameter to search inside that archive.

Normally you would instead use the homepage URL where WP will then load the search.php template and do a full search