In Blueprint Editor Settings, “Hide Unrelated Nodes” was turned on by default, so I turned it off. But without effect. My BP Editor still looks like this. I don’t want the opacity of unrelated nodes fading out.
This is wild. It does not apply “Hide Unrelated Nodes” when a BP class is opened WHILE changing something in Editor Preferences. So I closed all BP classes and set “Hide Unrelated Nodes” to false, and - in a magical way that is hidden in the depths of the engine - it worked after restarting the Editor.