It´s Editor only, not runtime.
For “GetActorsFromDataLayer” you are using the “DataLayerEditorSubsystem”…
While for the BP-Nodes which are available, you are just using the “DataLayerSubsystem” (without Editor) ^^
Check those links for the difference:
I don´t know why they are editor-only, because it would be a high performance-boost, if you could add actors to data layers at runtime…