Using New Outlook on Windows for personal email, calendar, and contact management
I got it to work!
open outlook, go to view settings (under view header at top next to home)
click General
Click privacy and data
Scroll down to privacy Settings, click
Scroll down and turn on experiences that analyze your content at the bottom of page, DO NOT click the very bottom one unless you want that too.
click close.
Recheck an email with the spell check, word should show up in red shade. I got lucky with the General heading.