We believe that we replied you to your E-Mail and Support Ticket. Please mention the Theme Name during seeking any support because we have 35 Themes.
That options is not for posts, that is for pages. If you really want to hide the featured images from the posts you can paste the following red color code in the NewsPress Options > General Options > Custom Code within Head Area Box
<style> .attachment-single-page { display: none; } </style>
