Hey there @martyysmart! I’m not super involved into the tools development but I believe the node you’re looking for is the Filter by class node as you say. Filter array is usable in game, but filter by class is editor utility only, so you should be able to access it while working on an editor utility BP or an editor utility widget BP. If you cannot see it while working on the editor utility, try unlocking the context menu, it sometimes gets in the way for me.
Here’s the documentation reference: Filter by Class | Unreal Engine Documentation
Let me know if you have any questions!