@weirdwriter right! So when I posted those screenshot, the ordering would have been the header, avatar, display name and username, then the section with (pinned) toots, followed by the profile fields and bio. Which also matches how it's laid out visually, from top to bottom, and left to right.
I tried out moving the bio column to the left though, and visually people seem to prefer that as well, and that ordering also makes more sense for screen readers I think, like you mentioned.

My comment about discrepancies between DOM and visual ordering is also not an issue then, as they're moved to the left/start for both.

In the general sense, DOM elements are ordered from top to bottom, and if there's space, can go left to right before wrapping further down. But there are ways to radically change the visual order, through CSS and other attributes, which can cause confusion for people who use screen readers combined with visual perception, as now jumping to the next element does not match the expectation.