@PumpkinsLinked So I think you just need to drag actor.gd onto Player.
@PumpkinsLinked Each object in your tree has a type. The one that looks like a person icon is a KinematicBody2D. That's the player object that I think you are trying to drive with your script.
You can see the node type if you hover over the name in the scene tree.
If your .gd script 'extends' KinematicBody2d, those are the only objects it could be assigned to. In godot every object is of a certain type, and an assigned script is like overriding that specific type with new behavior.
@PumpkinsLinked I'm learning myself so don't get what I'm saying too seriously. I've copied your code and my square moves. I've seen in your third screenshot the script is not attached to anything. Maybe it's that?
@PumpkinsLinked I don't see a script attached to any of the objects in your scene tree, so I don't think its even running.
The warning you are getting in the log isn't really important, but can sometimes catch when you meant to do more with a function than just run it.
You can turn off the warning, amongst others, in the settings.