Hi,
Sorry for the late reply.
Unfortunately, it’s not possible to achieve this layout (multiple 3 columns grid turning to 2 columns) with the Columns block.
To create a single “card with shadow” block, you can use the Columns block and set its column number to 1. Then adjust the column width as you like. And if you need to center it, add the tw-justify-center class in the “Additional CSS Class(es)” field of the columns block.
The following code can help you start:
<!-- wp:columns {"className":"tw-justify-center","twColumnStyle":"card-shadow"} -->
<div class="wp-block-columns tw-justify-center tw-cols-card tw-cols-card-shadow"><!-- wp:column -->
<div class="wp-block-column"><!-- wp:image -->
<figure class="wp-block-image"><img src="https://s.w.org/images/core/5.5/don-quixote-02.jpg" alt=""/></figure>
<!-- /wp:image -->
<!-- wp:heading {"level":3} -->
<h3>Single Card</h3>
<!-- /wp:heading -->
<!-- wp:paragraph -->
<p>Lorem ipsum dolor sit amet, commodo erat adipiscing elit. Sed do eiusmod ut tempor incididunt ut labore et dolore.</p>
<!-- /wp:paragraph --></div>
<!-- /wp:column --></div>
<!-- /wp:columns -->
I hope the above is useful to you.
Tom