Why this theme broke at .org?

Hi there,
I suggest changing the featured image size to your preference, so
you can open functions.php file and locate
set_post_thumbnail_size( 665, 435, true );
then change it to
set_post_thumbnail_size( 665,1000, true );

then install the Regenerate thumbnails plugin, activate it and go to Tools -> Regen. Thumbnails to run a regeneration in order for the change to be applied.

Now the main difference between the two sites is that in the first one you are not using a featured image and you are showing the full content from Appearance->Customize->Layout Options (Display the excerpt instead of the content.) while in the second you are rendering the excerpt with the featured image (which is small).

Let me know if this works

I works with the first post, but when I have other feature images like square or anything else it zooms the picture to the size I was adding. How can I do it that keep the image if it is square, vertical or horizontal in the size that at https://www.balazszsalek.com ?

Hi there,
you should remove cropping by changing

set_post_thumbnail_size( 665,1000, true );

to
set_post_thumbnail_size( 665,1000, false );

OR ( what you have https://www.balazszsalek.com )

Remove featured image, and check Display the excerpt instead of the content in order to show the full content from Appearance->Customize->Layout Options.
Then Add a regular image in your content editor before any other content which will serve as a featured image. Use “Read More” tag to control how much content you want to show in the frontpage (https://www.wpbeginner.com/beginners-guide/how-to-properly-use-the-more-tag-in-wordpress/)

Let me know if this works, or if I can help out more.