Featured image in posts is dark: how to change?

I’m setting up the Twenty Twenty-Three theme in a child theme on a staging site behind a login, not my live site. I can’t see how to change the style for showing a featured image in a post without what looks to be a filter or something that dims the image. This is only the case with the featured image – other images in a post appear normally.

Is there a setting somewhere to make the change?

Thanks!