2D object not rendered in 2D editor viewport of they are chidren of a SubViewport

[blackears]

Godot version

v4.0.rc1.official [8843d9a]

System information

Windows 10, Compatability

Issue description

Nothing is rendered in the Godot editor if you are editing a 2D scene that is a child of a SubViewport node.

Steps to reproduce

Create a new scene with a Node3D root node.
Add a Node2D as a child.
Click on the Node2D. Godot will switch to 2D view.
Add a Polygon2D as a child of the Node2D. Draw a polygon. You will see the results in the viewport.
Add a SubViewport node as a child of the Node3D
Drag the Node2D so that it is a child of the SubViewport.
Click on the Node2D again. Now nothing is rendered in the viewport.

Minimal reproduction project

2dIn3D.zip

[Sauermann]

Please have a look at #50185

[KoBeWi]

SubViewports do not display anything on their own, you need SubViewportContainer or ViewportTexture.
Also duplicate of #20619