The Portfolio Analysis tool in Project Online and Microsoft Project Server is a VERY sophisticated tool, and is intended for organizations that want to optimize their project intake process. Microsoft has developed some fairly good documentation on this tool at:https://docs.microsoft.com/en-us/projectonline/portfolio-analysis-overview
In their web site, be sure to read all of the articles related to this topic, including how to set up the tool. Also, if you do a Google search for "Portfolio Analysis tool in Project Server", you will find multiple links to YouTube videos on the subject. I have not watched any of these videos personally, so I cannot recommend any of them for you.
Hope this helps.