you can hide the featured image from you post but keep it as the thumbnail for your category page by using CSS
Go to “Theme Options” and then “Layout Setting” and then type type into the “Custom CSS” window this code:
.post-thumb {
display: none;
}
This will hide the featured image from the actual post page, but will allow it to still be visible when you look at the thumbnail in any of the category sections.
I tested this out, and it seems to work for me.
https://www.lifeontheyamanote.com/category/one-day-trips/ (go ahead an click on the single post on this page and you will see the featured image is gone)