Environment: Background Mode: Canvas causes Popup windows to become severely transparent (including default "ToolTip") regardless of `background_canvas_max_layer` property

### Tested versions

- Reproducible in Godot 4.3 (Renderer: Mobile)

### System information

Windows 11 - Godot Engine v4.3.stable.official.77dcf97d8 - https://godotengine.org Vulkan 1.3.278 - Forward Mobile - Using Device #0: NVIDIA - NVIDIA GeForce RTX 3050 Laptop GPU

### Issue description

When using World environment in a scene, and setting the background mode of an environment to `canvas`, every popup window (transparent = true) to become severely transparent (almost invisible) Even when the theme is custom set to be fully opaque have tried to change the CanvasLayer's `Layer` which is the parent of the GUI node to a higher value than the `background_canvas_max_layer` but it has no effect.


EXPECTED OUTCOME (WorldEnvironment `Background Mode` set to: `Clear Color`):

If this is the intended behavior, please tell me how to turn the severe transparency off for the default tooltip since i am overriding it with my own using `_make_custom_tooltip()` (even though the issue still exists with the default ones). thank you.

### Steps to reproduce

1. Create a new projectin godot 4.3 (Mobile)
2. Make a 2D scene:

3. Add a `WorldEnvironment` Node as a child.
4. Add a new environment and in the "Background" subgroup in the editor, Change the mode to `Canvas` and set `Canvas Max Layer` to 1:

5. Add a `CanvasLayer` as the Child of Root `Node2D`. Set the `Layer` to anything greater than 1 (5 in my case):

7. Add a `PanelContainer` as the child of `CanvasLayer`. Set the `TooltipText` to any text in the editor:

8. Save and Run the Scene and Hover your mouse cursor over the `PanelContainer`. The (More) Transparent Tooltip Text will be displayed:

9. Now Change the Background Mode of the `WorldEnvironment` to anything other than "Canvas".

10. Save and Run the Scene. Now the Popup (Tooltip) is being displayed as Intended:

### Minimal reproduction project (MRP)

[mrp-bg_canvas.zip](https://github.com/user-attachments/files/18221440/mrp-bg_canvas.zip)