Restrict search results to a specific Post category

I created a search and shortcode that I included on a page. I wanted to restrict search results to a single specific category.

Unfortunately, I keep getting results from the complete site. I tried the regular engines well as the indexed engine and both work the same.

I followed the instructions here
https://documentation.ajaxsearchpro.com/frontend-search-settings/category-and-taxponomy-term-filters
but this did not work either

This is the search field:

Cégajánló

(just above the footer)
The search in the header is the global search and is supposed to search the whole site.

I found some examples on your site, but all were filters in functions.php to restrict result entries to the current category. What I’m looking for is the stock functionality in the GUI. It must be a single trick that I’m missing, however, both of us IT professionals have not been able to find it since last week.

If you must have the admin access I will send it, but first please share the trick to accomplish this simple task with us. Maybe the admin code will not be needed.

Thank you