Blurring with SubViewport in Godot

Godot Version

Godot 4.2.1


When I add a SubViewport node to a 2D scene and render a 3D scene with the SubViewport , scaling the window causes the 3D scene to become blurry:

I tried to change the project settings for display/window/stretch/mode and display/window/stretch/aspect to canvas_items and expand respectively:

But the SubViewport still blurry. I expect the content within the SubViewport to be as clear as when running the 3D scene independently: