I have a similar question. I have UILabels which I use as headings (setting their accessibilityTraits to .header). I thought that I could establish some sort of header hierarchy by setting each one's attributedText to an attributed string which had .accessibilityTextHeadingLevel applied to its entire range ... but that doesn't appear to result in any difference in the accessibility experience.
What effect is .accessibilityTextHeadingLevel supposed to have? I see documentation on how to set it, but nothing saying what it actually does.