Gui in 3D Demoproject no longer works

[Sauermann]

Which demo project is affected:
https://github.com/godotengine/godot-demo-projects/tree/master/viewport/gui_in_3d

OS/device including version:
Debian 12, X11, Xfce

Issue description:
The demo project "Gui in 3D" no longer works in v4.2-dev6.
Instead of the usual screen, only a gray background is displayed.

I would expect, that the demo project works and its content is shown.

Bisecting shows that it no longer works since godotengine/godot#80813.

[GeorgeS2019]

We need a few more examples of 3D GUI, if possible, one that demonstrates 2D charts in 3D Gui

[GeorgeS2019]

Just realized this could be relevant

[Alex2782]

Does this demo need to be ported?
The 3D camera is positioned incorrectly (animated)

[Alex2782]

This is how the animation looks in version 4.1.2.
In version 4.2 beta (1 and 2), the animation no longer works, always (0,0,0) position, behind the 2D GUI

Screen-2023-10-20-012815.mp4

[KoBeWi]

This looks like a regression in the engine.