How can I deselect Text in the outliner?
bpy.ops.object.select_all(action='DESELECT') will not work for this. I can just click with the mouse on Plane in the outliner and it works, but I want to do this in Python and didn't find a way yet.
That highlight is indicating the current active object. I was about to tell you that you can't really do that, since most of that data is read-only, but after some stubborn, extra googling, it turns out you actually can!
bpy.context.view_layer.objects.active = None
I guess we both learned something new today.