Gadget export
To export the CollapsibleNav gadget, click on "Download" button, save the downloaded file, go to Special:Import on the destination wiki and upload it. Then add the following to MediaWiki:Gadgets-definition page:
* CollapsibleNav [ResourceLoader |dependencies=jquery.makeCollapsible, mediawiki.storage |skins=vector, vector-2022] |CollapsibleNav.js |CollapsibleNav.css
You must have appropriate permissions on the destination wiki (including the right to edit system messages) and import from file uploads must be enabled.