Per https://developer.mozilla.org/en-US/docs/Web/HTML/Element/header and https://www.w3.org/WAI/ARIA/apg/example-index/landmarks/HTML5.html <header> should carry the banner landmark role, when in context of the body element. The header element is not a banner landmark when it is a descendant of the following HTML sectioning elements: article, aside, main, nav, section. This is not currently how VoiceOver + Safari implements this. Any header element seems to generate a landmark banner role, irrespective of being positioned inside of article, aside, main, nav, section elements. Interestingly this is correctly implemented for sections. As you can detect with the rotor and landmark navigation in the the included example, the header element inside of a main is presented as a landmark, yet the header inside of a section is NOT a banner landmark in the landmark navigation.
<rdar://problem/96942150>
Created attachment 460851 [details] index.html with 3 header elements within different parents
Pull request: https://github.com/WebKit/WebKit/pull/22499
https://bugs.webkit.org/show_bug.cgi?id=195010
Committed 273188@main (da3bbf117740): <https://commits.webkit.org/273188@main> Reviewed commits have been landed. Closing PR #22499 and removing active labels.
See WPT review changes requested https://github.com/web-platform-tests/wpt/pull/44080#discussion_r1458126371