Using mw-collapsible class as described in https://www.mediawiki.org/wiki/Manual:Collapsible_elements auto-generates an anchor element <a class="mw-collapsible-text">Expand</a> to toggle collapse or expand the section.
This anchor element however is reported as an error by Google Lighthouse / Google Pagespeed https://pagespeed.web.dev/ . Error "Links are not crawlable". The anchor tag is auto-generated with JavaScript, but Lighthouse / Pagespeed renders this JavaScript before evaluating the page.
This error is due to Lighthouse needing a href attribute because it default interprets every anchor as a link. If no href attribute is present it registers the anchor as an error because it supposes it to be a crawlable link.
The implementation in MediaWiki is not wrong by HTML standards but it's not best practice and it might impact Lighthouse performance which is not optimal.
Our suggestion: Please add the attribute role="button" to the auto-generated link. The result would be <a class="mw-collapsible-text" role="button">Expand</a>. This is cleaner by HTMl standards and best practices and also prevents any Lighthouse errors which was already tested with Lighthouse locally.