fixes #66902

src/vs/base/browser/ui/tree/abstractTree.ts

@@ -511,6 +511,7 @@ class TypeFilterController<T, TFilterData> implements IDisposable {
 
 		const onDragOver = (event: DragEvent) => {
 			const x = event.screenX - left;
+			event.dataTransfer.dropEffect = 'none';
 
 			if (x < midContainerWidth) {
 				positionClassName = 'nw';
@@ -1050,4 +1051,4 @@ class TreeNavigator<T extends NonNullable<any>, TFilterData, TRef> implements IT
 		this.index = this.view.length - 1;
 		return this.current();
 	}
-}
+}
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