If you want to disable featured image in post or page you can paste the code below in ‘custom CSS code’
.single-post .attachment-post-thumbnail {
display: none;
}
.post.has-post-thumbnail {
padding-top: 4%;
}
We have checked this with WordPress Twenty Sixteen theme.
Source: https://wordpress.stackexchange.com/questions/219440/hide-featured-image-in-post-in-twenty-fifteen
