How do I get a viewport frame to work on a brick?

Hi, I'm trying to make a camera system on a brick in a game rather than just setting the player's camera's CFrame. I can find videos that have viewport frames working on bricks, and there's multiple portal games that seem to work, but when I try adding in a viewport frame it doesn't work. When I drag the viewport frame into a screengui it works, so I can't really understand why it doesnt in a surface gui.