Godot 4 PackedScene extension to get export property value based on property name.

PackedSceneExtension.cs

public static partial class PackedSceneExtension
{
	public static Variant? GetNodePropertyValue(this PackedScene packedScene, int nodeIndex, StringName propertyName)
	{
		SceneState sceneState = packedScene.GetState();
		int propertyCount = sceneState.GetNodePropertyCount(nodeIndex);

		for (int propertyIndex = 0; propertyIndex < propertyCount; propertyIndex++)
		{
			if (sceneState.GetNodePropertyName(nodeIndex, propertyIndex) == propertyName)
				return sceneState.GetNodePropertyValue(nodeIndex, propertyIndex);
		}

		return null;
	}
}