What do you mean by archive? Structured discussions auto-archive old topics by surfacing the most active ones.
Do you mean resolving topics?

No, I mean the feature that allows users to archive the current wikitext talkpage and replace it with a StructuredDiscussions board.

You mean it is posible to convert a given page to Structured discussions even if that page is protected. That move is only possible for admins.

Indeed, as shown on https://www.mediawiki.org/w/index.php?title=Project_talk:Sandbox&action=unprotect, where anyone can edit, but only admins may move the page.

Only admins can move Structured Discussion pages or move any protected against moving pages. So I'm not sure to understand what is the problem? :)

I'm sorry if I haven't been clear enough. The problem is that regular users can use Special:EnableStructuredDiscussions to enable Structured Discussions on a page, even when that page is protected against moving. They should not be able to enable Structured Discussions because the current page would be moved, which it is protected against. Yet they can. I've tested this with a user page of mine: https://www.mediawiki.org/wiki/User:Mainframe98/Flow_move_test. My bot-account, which is not an administrator, nor has any rights outside autoconfirmed was able to archive the page and replace it with a Structured Discussions page even though I had protected the page against moving by anyone not an administrator: https://www.mediawiki.org/w/index.php?title=User:Mainframe98/Flow_move_test/Archive_1&action=history
I hope this illustrates the situation a bit more clearly.

I've rephrased a bit the title and the description to make it actionable.

I've also created a new ticket to explore possible limitations for page creations on wiki that have SD as the default discussion system: T177504: Only allow admins to create Structured Discussion boards on wikis where Structured Discussions are enabled by default