first

wp-content/themes/twentytwentyone/template-parts/excerpt/excerpt-image.php

@@ -0,0 +1,21 @@
+<?php
+/**
+ * Show the appropriate content for the Image post format.
+ *
+ * @link https://developer.wordpress.org/themes/basics/template-hierarchy/
+ *
+ * @package WordPress
+ * @subpackage Twenty_Twenty_One
+ * @since Twenty Twenty-One 1.0
+ */
+
+// 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();