The bubble gum simulator doesn’t look like it uses ViewportFrame, the rendering is way too nice for a ViewportFrame.
Based on the post ViewportFrame release, it has been mentioned that neon does still render on the lowest quality.
The only workaround I can think of are to add blurry layer to recreate the neon effect, or if you still want to use “green screen”, but changed to blue or red, as long as it’s contrast to the object. The limitation is that it will have hard time to properly render your cute rainbow creature.