What's going on with the size of my video, man?

Shot with an iPhone 13 pro in 4k 60, I am having an issue with the size of the final product as shown in the screenshot. I’ve adjusted the resolution and aspect ratio (1920x1080, 30fps), but I’m still getting a small, almost “vertical” rendering of my video. I even had to convert the videos, and those still have the playback in a smaller scale.

Any thoughts?

Your Settings > Video Mode is wrong. It is like choosing the wrong paper size in print work.