[NSFW] Remove featured image on single course pages

Above example of a single course page on my site. I want to remove the small image underneath the ‘Teacher, Categories, Review’ info. When editing the course in Learnpress this image is set as the ‘featured image’. If I remove the featured image I then face the problem of it also removing the image on the page showing the full course selection (e.g. https://online-training.touchofhappiness.co.uk/lp-courses/). Is there a way to not show the featured image on the single course page, but still keep it in the listings of all courses? I have tried to use this CSS that was suggested in a previous posting on this topic:

body.single-lp_course .post-thumb-img-content.post-thumb {
display: none;
}

Unfortunately it doesn’t do the job. Nothing changes. What can I do?

The page I need help with: [log in to see the link]