Using New Outlook on Windows for personal email, calendar, and contact management
No, I have 365 Family. The suggestion below, submit by someone else fixed the problem.
jasonlacarl has replied to the question No spellcheck in new outlook Editor greyed out that you are following in Microsoft Support Community.
In new Outlook.
Navigate to Settings > General > Privacy and Data > Privacy Settings.
Enable Turn on experiences that analyze your content.
This fixed it for me. No idea how that setting got changed or if its new or something.