Your Godot version:
4.3

Issue description:
Section entitled "Necessary code" is incorrect or godot has a bug. A VBoxContainer was created in a scene with a root Control node. the VBoxContainer contains 4 buttons with a custom theme set. The Control has a script:

func _ready():
	$StartButton.grab_focus()

The scene was instantiated and added to an active scene that has a Node2D root node.

This does not appear to result in the StartButton taking focus. Instead, it appears it is necessary to set focus somewhere in _process() or with a timer signal.

URL to the documentation page:
Necessary code¶