TL;DR- I'll save people's time by saying this; I followed the Microsoft steps to the T and got absolutely no where.
For the long read-
So I followed your guidance to "how do you add/turn on microsoft editor for email". This had two options based on whether Editor was there or not. John's issue, as well as my own, and seems to be everyone else's is that Editor is not in the ribbon where you, and all the other bots, say it should be.
The guidance for no Editor was to go to "how to clear your cache" and to open Chrome, go to the three dots in the top right of the browser. Open Extensions, check to see if Editor is there (as it seems Chrome and Outlook do not automatically come with the add-on for spell check... ridiculous).
Once you see Editor isn't already installed, open "Discover more extensions and themes on the Chrome Web Store". Search "Microsoft Editor" and add it to your extensions.
From there, it says to close out, go into the web browser and see if it magically pops up to the left of Check Accessibility (where it should have already been). If, and when, it's not there, make sure your version is totally up to date with the version it should be and then silently rage to yourself for wasting your time.
None of these steps worked for me, and the only other option was to reach out to Microsoft Support Team to provide feedback, remotely help, collect logs, and involve more resources to investigate the issue from backend side.... Which does us no good until they decide to just GIVE US BACK SPELL CHECK IT NEVER SHOULD HAVE BEEN REMOVED!