Good question. Keep in mind that I do not work for Microsoft and am not in charge of the Microsoft Docs site, but it appears that the documentation in that site is not for "end user" applications, such as Word or Excel. When you use the term "Project", I assume you are talking about the new Project for the Web application. That tool is also an "end user" application, which I suspect is why there is no documentation for it in the Microsoft Docs site. On the other hand, if you select the Project Operations topic under the Dynamics 365 section, you will find a lot of documentation about D365 Project Operations, which is actually the "back end" application for Project for the Web.
If you are looking for a document that describes how to use Project for the Web to manage projects, you might check out the eBook I wrote while working at my former employer at: