* @link https://developer.wordpress.org/themes/basics/template-hierarchy/

* @package WordPress

* @subpackage Twenty_Twenty_One

* @since 1.0.0

// If there is no featured-image, print the first image block found.

if (

! twenty_twenty_one_can_show_post_thumbnail() &&

has_block( ‘core/image’, get_the_content() )

twenty_twenty_one_print_first_instance_of_block( ‘core/image’, get_the_content() );

the_excerpt();

The code is self-explanatory, but let’s take a closer look:

* has_block determines whether a post or a string contains a specific block type (the core image block in this example).

* twenty_twenty_one_print_first_instance_of_block is a Twenty Twenty-One template function that prints the first instance of a block in the content and then breaks away.