Calling add_child() during NOTIFICATION_WM_ABOUT always gives "Parent busy setting up children" error

[MewPurPur]

Tested versions

Reproduced in 4.3

System information

Godot v4.3-stable - macOS 15.2.0 - Vulkan (Forward+) - integrated Apple M3 - Apple M3 (8 Threads)

Issue description

Seems like a pretty trivial use case to add an AboutMenu kind of node for NOTIFICATION_WM_ABOUT. But no matter what node I add it to, I get the same error, "Parent busy setting up children, add_child() failed. Consider using add_child.call_deferred(child) instead". So this is easy to workaround, but also seems like it shouldn't happen.

Steps to reproduce

See the MRP.

func _notification(what: int) -> void:
	if what == NOTIFICATION_WM_ABOUT:
		var texture_rect := TextureRect.new()
		texture_rect.texture = load("res://icon.svg")
		add_child(texture_rect)
		#add_child.call_deferred(texture_rect)

Minimal reproduction project (MRP)

MacOSbug.zip

[MewPurPur]

I believe this is also platform:macos because it seems like a MacOS-exclusive notification.