(Change) featured image size in post

please share a link to your page.

May I ask where you need this for? I assume you also use the theme itself.

The link to the page showing the stretched issue.

Ok. Link!

You can see two featured images of two posts. One – the photo – I can’t find on my messages list at the dashboard. But that is another problem.

If you’re not using a Child Theme, and if the theme doesn’t have a designated section of the dashboard for CSS modifications then do the following:

1. Install this Custom CSS Manager plugin https://www.ads-software.com/plugins/custom-css-manager-plugin
2. use its “CSS Code” section of the dashboard to hold your CSS modifications:
3. (put this code in)

   img.archive-image {
       width: auto;
   }

4. Save

Alternatively use your Child Theme style.css file to hold your CSS modifications

Aha! Adrew, you’re my star of the day.
Thanks.

Problem solved:
> Add the above code to the style.css in the child theme.