Highlighted image wrongly resized

Whenever we create a new post and add a highlighted image, this image is shown in the “category blogs” just as it was meant to be, with the appropriate size in the main page. On the contrary, when we access the post itself, the image is resized and becomes very big
Please find attached a screenshot of this situation (In the first image it’s ok since it is located in the blog category, but the second image, within the post, shows how large it gets ( far too big, huge I’d say)