Hello, @Martin,
Actually, It’s not a theme issue it is a server configuration issue nothing else and only from the server, you will be able to fix it. Please check this article: https://www.wpbeginner.com/beginners-guide/how-to-add-http-security-headers-in-wordpress/#:~:text=Adding%20HTTP%20Security%20Headers%20in%20WordPress%20using%20Cloudflare&text=Once%20Cloudflare%20is%20active%20on,the%20%27Enable%20HSTS%27%20button. For a better reference to understand how to fix it.
Regards 8Themes Team.
