only add culture to the preview url if the document can vary

src/Umbraco.Web.UI.Client/src/packages/documents/documents/workspace/document-workspace.context.ts

@@ -596,8 +596,15 @@ export class UmbDocumentWorkspaceContext
 		// Tell the server that we're entering preview mode.
 		await new UmbDocumentPreviewRepository(this).enter();
 
-		const preview = window.open(`preview?id=${unique}&culture=${culture}`, 'umbpreview');
-		preview?.focus();
+		const previewUrl = new URL('preview', window.location.origin);
+		previewUrl.searchParams.set('id', unique);
+
+		if (culture && culture !== UMB_INVARIANT_CULTURE) {
+			previewUrl.searchParams.set('culture', culture);
+		}
+
+		const previewWindow = window.open(previewUrl.toString(), 'umbpreview');
+		previewWindow?.focus();
 	}
 
 	async #handleSaveAndPublish() {