How do I stop avatars from being visible?

So I have a video explaining my problem. Basically, if I want to have a 2D game with a ScreenGui that’s fullscreen, a player’s avatar is visible for a brief moment, as you can see in the video. Does anybody have any ideas to make it so that they can’t see the 3D world when readjusting the window size?
Screen Recording (1-17-2021 2-55-17 PM).wmv (1.7 MB)

I don’t think this is fixable - it seems like an issue with Roblox, as the UI needs to adjust to the change in screen size.

You could try making everything invisible and adding a completely white skybox - that’s the only plausible solution I can think of.