why is categories greyed out in outlook?

Outlook is a Microsoft product, not an Apple product, and there are not as many Office users active here as one would think. MS Office questions posted in Apple’s forums can linger here a long time in many cases.

Start here: 

https://answers.microsoft.com/en-us/msoffice

Be sure to include "mac" in your search string to limit the search to Outlook Mac topics. Same if you post a question—include "Mac" in the title. That makes it easier for other Mac users to search for new posts.

I believe you will find the contributors there knowledgeable and very helpful, much more so that MS's Windows-centric support documents.Stat here:

With no response here in a day, I suggest you visit an Outlook user forum.