I have noticed that when I view a Doc on the mobile app, Columns stay horizontal instead of auto-stacking in some way. Because they stay in a horizontal row, the columns become so squished together the text is unreadable. It would be great if the columns would auto-stack when the viewport got too small or when on mobile, so that they can be actually readable.

A "Table" will sort of fix this problem, but on mobile, you have to swipe to see the entire contents, which makes sense for showing multiple rows, but unnecessary with a column layout.