Just to be clear, are we talking about this list? (screenshot from https://en.wikipedia.org/w/index.php?title=Aaart.edu&action=submit)

I don't really understand why you would want it to be removed/hidden (it is already collapsed by default).

Hidden categories become visible now.

• Is that intended?
• Did that has been all the time?
• IIRC some decades ago they were hidden for those who did not opt in.

I did some digging and it seems the feature was introduced in 2008 (rSVN31257) and the list has always been displayed there since then (although originally it wasn't collapsible).

• action=info does not mention any hidden for anybody (is that intended, BTW?)

Actually, I see the list of hidden categories on https://en.wikipedia.org/w/index.php?title=Aaart.edu&action=info:

Yes, we are talking about the same issue.

It does not matter much whether the list items are folded or expanded.

The issue is whether a user, e.g. a newbie, who is not supposed to deal with hidden things and who has no access to them on regular page view (and VE?) suddenly might be confused by maintenance things never heard of?

The other collapsed things like transclusions, wikidata ingredients and performance metrics may be useful, or not, but those are visible (at least external resources) in pageinfo story.

But here suddenly categories arrive on source editing which vanish again after publishing, not listed among all other categories. If I look through the eyes of a newbie I would be confused.