FAQ Structured Data From Details Blocks

add_action( 'wp_head', function () {
    if ( ! is_singular() ) {
        return;
    }

    $post = get_queried_object();

    if ( ! $post instanceof WP_Post || ! has_block( 'core/details', $post ) ) {
        return;
    }

    $questions = array();
    $html_of   = function ( $blocks ) use ( &$html_of ) {
        $html = '';

        foreach ( $blocks as $block ) {
            $html .= $block['innerHTML'] . ' ' . $html_of( $block['innerBlocks'] );
        }

        return $html;
    };
    $walk      = function ( $blocks ) use ( &$walk, &$questions, $html_of ) {
        foreach ( $blocks as $block ) {
            if ( 'core/details' !== $block['blockName'] ) {
                if ( ! empty( $block['innerBlocks'] ) ) {
                    $walk( $block['innerBlocks'] );
                }
                continue;
            }

            if ( ! preg_match( '#<summary[^>]*>(.*?)</summary>(.*)#is', (string) $block['innerHTML'], $m ) ) {
                continue;
            }

            $question = trim( wp_strip_all_tags( $m[1] ) );
            $answer   = trim( preg_replace( '/\s+/', ' ', wp_strip_all_tags( $m[2] . ' ' . $html_of( $block['innerBlocks'] ) ) ) );

            if ( '' !== $question && '' !== $answer ) {
                $questions[] = array( '@type' => 'Question', 'name' => $question, 'acceptedAnswer' => array( '@type' => 'Answer', 'text' => $answer ) );
            }
        }
    };

    $walk( parse_blocks( $post->post_content ) );

    if ( $questions ) {
        echo '<script type="application/ld+json">' . wp_json_encode( array( '@context' => 'https://schema.org', '@type' => 'FAQPage', 'mainEntity' => $questions ), JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE | JSON_HEX_TAG ) . "</script>\n";
    }
} );