I don’t have a Roku TV but “stretch” normally stretches a 4:3 image to 16:9 by making everything and everyone in the video look wide/fat. Zoom normally enlarges the image in all directions so that everything maintains proper proportions, but in order to do that, it has to cut off the top and bottom of the 4:3 source material. (So the tops of heads may be cut off etc.) “Normal” usually just displays the 4:3 image with pillar boxing – black or gray bars on the side. There is no perfect solution to putting 4:3 on a 16:9 screen which is why TVs give you options and let you sort out which is the least bad in your opinion. For me, normal with pillar boxes is the least bad. (It also makes the resolution limitation of a DVD less obvious on a big screen.)
They won’t hurt your TV. It’s just software.
