How to create custom dashboards
Custom dashboards can be registered using a package.manifest or using code.
You are currently looking at documentation for Umbraco 8 and older versions.
An automated guess is that docs.umbraco.com/umbraco-cms/reference/configuration-for-umbraco-7-and-8/dashboard/ could be the link to the new documentation for Umbraco 9 and newer versions.
Custom dashboards can be registered using a package.manifest or using code.