Hi @voodmook,
Thank you for contacting us.
I used Google translate as I only speak English, your query more/less reads:
The theme gives me the option to put a fixed header, but when I activate the option nothing happens, it is as if it was not activated
I visited your site and did quick checking with my web browser’s source code viewer. At the most bottom line shows <!-- Cached page generated by WP-Super-Cache on 2022-01-18 21:58:28 -->, that indicates you’re having an active cache.
Perhaps the cache retains the old pages (before changes) to load on web browser. Please flush it and reload your page. Also, you may need to clear saved site’s data, history, and cache on your web browser as well.
Adding, visit this article for further information about this case.
Hope this reply helps.
Regards,
Kharis
