Format of featured image when using show_posts

[travincult]

I would like my featured image on single post pages to be full width (as large as the image is) instead of being shrunk to the width of the rest of the post. Like here: https://travelinculture.com/itinerary-queensland-in-australia/. I have done this by hiding the featured image + title (display:none) on the single post page – and instead manually inserted an image which I force to full-width.
Now the problem is that I would still like to use this post (its featured image + title) in the [show_posts] shortcode inserted on other single post pages. However, when I try to do this the featured image is not shown (apparently since I have hidden it on the original single post page). Can’t I show the format from the blog category post page (on the page https://travelinculture.com/destinations/oceania/) when I insert it on other single post pages (using [show_posts])? How can I tweak it?
Alternatively, if this is not possible, can I use CSS code to enlarge all featured images on single post pages? (going a bit beyond/wider than the rest of the post?) I have tried in various ways – but without success.
Can you help me?

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