Instantiated Scene Nodes have Null Everywhere

Godot v4.2.2 .NET C#

Question

I want to do scene loading in C# (and I come from Unity).

When using the following code on a simple button press that I hooked up in the Inspector (Node panel, “pressed” signal), it seems to work by going from this,
image

to this:
image

But all my scripts have zeroed out and nulled out fields/variables in the inspector (my [Export] fields).
What am I doing wrong?

using Godot;

namespace RogueliteRPG {
    public partial class SceneTester : Node {
        [Export] private PackedScene nextScene;

        private void OnButtonPressed() {
            Node copy = nextScene.Instantiate();
            Owner.AddChild(copy);
        }
    }
}