diff --git a/backport-changelog/7.1/12004.md b/backport-changelog/7.1/12004.md
new file mode 100644
index 00000000000000..c7033525a085f7
--- /dev/null
+++ b/backport-changelog/7.1/12004.md
@@ -0,0 +1,3 @@
+https://github.com/WordPress/wordpress-develop/pull/12004
+
+* https://github.com/WordPress/gutenberg/pull/78404
diff --git a/lib/media/load.php b/lib/media/load.php
index cdd261158b43e0..b0cc5605b0dca9 100644
--- a/lib/media/load.php
+++ b/lib/media/load.php
@@ -295,6 +295,13 @@ function gutenberg_set_up_cross_origin_isolation() {
 		return;
 	}
 
+	// Skip when rendering the classic-theme home route, which shows the site
+	// preview in an iframe and must reach its `contentDocument` to neutralize
+	// interactive elements — DIP would block that.
+	if ( 'site-editor' === $screen->id && ! wp_is_block_theme() && ( ! isset( $_GET['p'] ) || '/' === $_GET['p'] ) ) {
+		return;
+	}
+
 	// Skip when a third-party page builder overrides the block editor.
 	// DIP isolates the document into its own agent cluster,
 	// which blocks same-origin iframe access that these editors rely on.
diff --git a/test/e2e/specs/site-editor/site-preview.spec.js b/test/e2e/specs/site-editor/site-preview.spec.js
new file mode 100644
index 00000000000000..200c6b5cce041e
--- /dev/null
+++ b/test/e2e/specs/site-editor/site-preview.spec.js
@@ -0,0 +1,42 @@
+/**
+ * WordPress dependencies
+ */
+const { test, expect } = require( '@wordpress/e2e-test-utils-playwright' );
+
+test.describe( 'Site preview', () => {
+	test.beforeAll( async ( { requestUtils } ) => {
+		// The site preview iframe is only rendered for classic (non-block) themes.
+		await requestUtils.activateTheme( 'twentytwentyone' );
+	} );
+
+	test( 'makes interactive elements inside the preview non-interactive', async ( {
+		admin,
+		page,
+	} ) => {
+		await admin.visitSiteEditor();
+
+		const previewFrame = page.frameLocator(
+			'iframe[title="Site Preview"]'
+		);
+
+		const interactiveSelector = [
+			'a[href]',
+			'button:not([disabled])',
+			'input:not([type="hidden"]):not([disabled])',
+			'select:not([disabled])',
+			'textarea:not([disabled])',
+		]
+			.map( ( selector ) => `${ selector }:visible` )
+			.join( ',' );
+		const interactiveElements = previewFrame.locator( interactiveSelector );
+
+		await expect( interactiveElements.first() ).toBeVisible();
+
+		const count = await interactiveElements.count();
+		for ( let i = 0; i < count; i++ ) {
+			const element = interactiveElements.nth( i );
+			await expect( element ).toHaveAttribute( 'aria-hidden', 'true' );
+			await expect( element ).toHaveCSS( 'pointer-events', 'none' );
+		}
+	} );
+} );