Right now there's just a "More" button, and once you click it there's no way to go back (apart from the browser's back button) and no indication that you're not on the first page. MediaWiki core has built-in standardized pagination controls, we should consider using those.
As part of this, drop the More button, including the AJAX appending of new notifications. Instead, users will always go page to page, until we do T129363: Pagination for the Notification Page.