Removing the image from post

Your question is very theme-specific, so it would actually be best placed in their support forum: https://ww.wp.xz.cn/support/theme/popularfx/

But I had a quick look at it. You are talking about the so-called feature image. This is always displayed in this theme in the places you have already noticed. There is no option to simply turn off the output.

You have 2 possibilities to adjust it to your wishes:

a) With the following code you can influence the output:

function popularfx_post_thumbnail() {
	if ( post_password_required() || is_attachment() || ! has_post_thumbnail() ) {
		return;
	}

	if ( !is_singular() ) : ?>

        <a class="post-thumbnail" href="<?php the_permalink(); ?>" aria-hidden="true" tabindex="-1">
			<?php
			the_post_thumbnail(
				'post-thumbnail'
				array(
					'alt' => the_title_attribute(
						array(
							'echo' => false,
						)
					),
				)
			);
			?>
        </a>

	<?php
	endif; // End is_singular().
}

This would need to be added to functions.php of a child theme, a custom plugin, or via code snippet plugin.

b) You could also hide the image via CSS. The following code for this:

body.single .post-thumbnail { display: none; }

You would have to insert this under Appeareance > Customizer > Additional CSS.

As said: if you have further questions, better ask in the support forum of the theme you are using.

Mmh for me both worked. So something is different with you than with my default installation only with this theme. Or you have not inserted the source code completely. By the way, you should never customize the files of plugins or themes unless it’s from you. Hence the reference to the child theme.

But yes, if a theme doesn’t meet your needs, you can choose another from the thousands of others.