SubViewport.size_2d_override does nothing when set in scene's _ready function

[AaronWizard]

Godot version

4.0.beta5.official (89a33d2)

System information

macOS 13.0.1

Issue description

I have a scene with a SubViewport in a SubViewportContainer. In the scene's _ready function I am attempting to set the SubViewport's size_2d_override property to a value smaller than the SubViewport/SubViewportContainer's size. e.g. The SubViewport's size is 512x512, while I'm setting it's size_2d_override to 100x100. This has no affect when the game runs; any children of the SubViewport are not scaled down properly.

This works fine if I set size_2d_override in the SubViewport's inspector. It also works fine if I resize it during the root's size_changed event.

Steps to reproduce

1. Create a new scene.
2. Add a SubViewportContainer to the scene root.
3. Add SubViewport to the SubViewportContainer.
4. Add a Sprite2D to the SubViewport.
   
5. In the SubViewport's inspector, set its size to 512x512 and set "Size 2D Override Stretch" to true. Do not set values for "Size 2D Override".
   
6. Add this script to the root node:

extends Node

@onready var _viewport: SubViewport = $SubViewportContainer/SubViewport

func _ready() -> void:
    _viewport.size_2d_override = Vector2i(100, 100)

Expected Result: When the project is run, the sprite inside the SubViewport is scaled to reflect its size_2d_override.

Actual Result: No scaling is applied to the sprite.

Minimal reproduction project

ViewportTest.zip

[Sauermann]

Workaround until the fix gets merged is to set it twice:

func _ready() -> void:
	for i in 2:
		_viewport.size_2d_override = Vector2i(100, 100)

[golddotasksquestions]

If someone who find this issue tries to do this (low res SubViewport in a high res game) in the editor, I listed the steps to follow here in the Reddit post.