Try dedicated action

Author: sirreal

src/wp-includes/block-editor.php

@@ -310,8 +310,8 @@ function _wp_get_iframed_editor_assets() {
 	$current_wp_script_modules = $wp_script_modules;
 
 	// Create new instances to collect the assets.
-	$wp_styles  = new WP_Styles();
-	$wp_scripts = new WP_Scripts();
+	$wp_styles         = new WP_Styles();
+	$wp_scripts        = new WP_Scripts();
 	$wp_script_modules = $wp_script_modules->clone_without_enqueued_modules();
 
 	/*
@@ -369,38 +369,25 @@ function _wp_get_iframed_editor_assets() {
 		remove_action( 'wp_print_styles', 'print_emoji_styles' );
 	}
 
+	add_action( 'wp_print_iframe_html', array( $wp_script_modules, 'print_import_map' ) );
+	add_action( 'wp_print_iframe_html', array( $wp_script_modules, 'print_head_enqueued_script_modules' ) );
+	add_action( 'wp_print_iframe_html', array( $wp_script_modules, 'print_enqueued_script_modules' ) );
+	add_action( 'wp_print_iframe_html', array( $wp_script_modules, 'print_script_module_preloads' ) );
+
 	ob_start();
-	wp_print_styles();
-	wp_print_font_faces();
-	wp_print_font_faces_from_style_variations();
-	$styles = ob_get_clean();
+	do_action( 'wp_print_iframe_html' );
+	$html = ob_end_clean();
 
 	if ( $has_emoji_styles ) {
 		add_action( 'wp_print_styles', 'print_emoji_styles' );
 	}
 
-	ob_start();
-	wp_print_head_scripts();
-	wp_print_footer_scripts();
-	$scripts = ob_get_clean();
-
-	ob_start();
-	$wp_script_modules->print_import_map();
-	$wp_script_modules->print_head_enqueued_script_modules();
-	$wp_script_modules->print_enqueued_script_modules();
-	$wp_script_modules->print_script_module_preloads();
-	$script_modules = ob_get_clean();
-
 	// Restore the original instances.
 	$wp_styles         = $current_wp_styles;
 	$wp_scripts        = $current_wp_scripts;
 	$wp_script_modules = $current_wp_script_modules;
 
-	return array(
-		'styles'         => $styles,
-		'scripts'        => $scripts,
-		'script_modules' => $script_modules,
-	);
+	return array( 'html' => $html );
 }
 
 /**

src/wp-includes/default-filters.php

@@ -373,6 +373,12 @@
 add_action( 'wp_enqueue_scripts', 'wp_enqueue_emoji_styles' );
 add_action( 'wp_print_styles', 'print_emoji_styles' ); // Retained for backwards-compatibility. Unhooked by wp_enqueue_emoji_styles().
 
+add_action( 'wp_print_iframe_html', 'wp_print_styles' );
+add_action( 'wp_print_iframe_html', 'wp_print_font_faces' );
+add_action( 'wp_print_iframe_html', 'wp_print_font_faces_from_style_variations' );
+add_action( 'wp_print_iframe_html', 'wp_print_head_scripts' );
+add_action( 'wp_print_iframe_html', 'wp_print_footer_scripts' );
+
 if (
 	// Comment reply link.
 	isset( $_GET['replytocom'] )