You should be familiar with single column web design already. It’s the default approach on devices with small screens. Almost every element is shown in a vertical stack, one after another.
This book suggests that you use the same layout approach even on larger screens.
The only requirement is that no element can sit side by side with another element.
One thing to note is that elements stacked on the depth dimension—that is, when one element sits on top of another—are allowed.
Another thing to note is that if two elements look side-by-side but are actually part of the same image, it doesn’t count.
Single column design is a technical limit, not a principled one.