No it goes in library.js since it's a server side hook. And you need to add the corresponding entry in plugin.json.
// library.js myPlugin.filterMiddlewareRender = async (hookData) => { hookData.templateData.user = await user.getUserData(hookData.req.uid); return hookData; }; //plugin.json "hooks": { "filter:middleware.render": "filterMiddlewareRender" ... }