There are some older posts on the this topic, but much has changed in the past year. It appears that web version of To Do (to-do.office.com) now supports categories (yay!). However it appears that the Android app still does not.
Is there a plan in the works to allow managing categories in the Android app? Also, bonus points if you group tasks by categories. I'm been doing this for years in Outlook to create a Trello/Planner experience far before Trello or Planner were a thing :)