Search Block query customization

add_filter( 'render_block_core/search', function( $block_content, $block, $instance ) {

	// Require CSS Classes
	if( empty( $block['attrs']['className'] ) ) {
		return $block_content;
	}

	// Gather Post Types From Prefixed CSS Classes
	$post_types = [];
	foreach( explode( ' ', $block['attrs']['className'] ) as $class ) {

		if( strpos( $class, 'post-type-' ) !== false ) {
			$post_types[] = substr( $class, 10 );
		}

	}

	// Filter By Active Post Types On Site
	$post_types = array_filter( $post_types, 'post_type_exists' );

	// Require Matches To Proceed
	if( empty( $post_types ) ) {
		return $block_content;
	}

	// Append Hidden Form Field(s) To Search Form
	$hidden_fields = [];
	foreach( $post_types as $post_type ) {
		$hidden_fields[] = sprintf(
			'<input type="hidden" name="post_type[]" value="%s">',
			esc_attr( $post_type )
		);
	}
	return str_replace( '</form>', implode( $hidden_fields ) . '</form>', $block_content );

}, 10, 3 );