That's not correct. There is no aria-open attribute and the summary implicitly has the correct ARIA state, aria-expanded, indicating that its details element is either expanded or collapsed.

There have been bugs in its implementation, particularly in Safari and differing between mobile and desktop Safari.

Perhaps you’re right. What I mentioned might have been an issue that has since fade due to browser and AT updates.

Thanks for correcting me.

Why would you need aria attributes if it's summary tag?

I presume it has to do with AT and how it typically interprets the tag. TBH IDK other than I’ve seen it come up in accessibility discussions / groups.