The Self section means this blueprint. If you look at the Unreal Engine 4 video you linked it doesn’t have a Self slot.
What you need to plugin, into the Self Slot is the mesh or actor that you want to perform this on. If you don’t do this, the game will refer to your UMG Widget.
I suggest trying to drag from the blue cast node pin, release and then search for the Get Number Materials. Perhaps the Self pin won’t appear in this case.
You can see that the node says that the target is Static Mesh Editor Subsystem. So target has to be that. Knowing that, you just need to right click and search for Get Static Mesh Editor Subsystem, and connect that to the target pin:
Hello, I am trying to use the static mesh editor subsystem for the purpose of generating collisions on large numbers of static meshes. Unfortunately, I cannot access that particular subsystem (context sensitive or not).
The class this is occurring in derives from Editor Utility Actor (also tried Editor Utility Actor Component).
Unreal version 5.0.2
I can see other subsystems in the node selection menu, just not the static mesh editor one.