My test site has a few blog posts with videos. When all the posts are shown at https://porkopolis.org/t1-2020/blog/ all posts correctly have their featured image and preview description shown, but the posts with a video have the entire video in full size displayed as well. You can see this even better at the category page https://porkopolis.org/t1-2020/category/video/ which also needs to be changed. I would like to not display these full videos except on their individual post page.
Also, I should mention that I am building this site as a GeneratePress child theme, intending to somewhat replicate (and then improve) my current live site at https://porkopolis.org/
I probably should have mentioned I’m still using the Classic Editor on this site. I did go to the page you suggested and added PHP snippet suggested and presto. Problem fixed brilliantly. This question is solved. THANKS!