For those without code access for any reason, there’s a Blueprint only method to render Widgets to a texture and use it in meshes.
The WidgetComponent, which is normally used to render 3D widgets in the world, does exactly that. It renders the widget into a texture and applies it to a plane. The cool thing is it exposes the texture, which you can get with Get Render Target.
Just be aware that the WidgetComponent only renders while its plane is being rendered. What I usually do is apply a custom invisible material to it (masked, with opacity 0) and parent it to the camera, so it’s always in view, but invisible.