You must do same thing as described…
Make sure Engine Content is visible, open the Engine materials folder, and open the Widget3DPassThrough Material Instance. In that material graph, take the “A” pin of the “Multiply” node connected to “Emissive Color” and reconnect it to the “SlateUI” texture parameter as shown in the attached screenshots.
But you must use material named Widget3DPassThrough_Masked and in this material set (General->Parent) edited Widget3DPassThrough! Works for me on 4.25.3.