It is with the deepest frustrations that I must report Microsoft has pushed out Copilot onto Microsoft Word no matter what your previous settings were. If you have Office because you paid for it/are on a family plan/have a work/school account, you can disable it by going to Options -> click on Copilot -> uncheck 'Enable Copilot'.
(Note, you may not see this option if you haven't updated lately, but Copilot will still pop up. Updating should give you this option. I will kill Microsoft with my bare hands.)
In addition, Google has forced a roll-out of it's Gemini AI on all American accounts of users over 18 (these settings are turned off by default for EU, Japan, Switzerland, and UK, but it doesn't hurt to check).
To remove this garbage, you must go to Manage Workspace smart feature settings for all your Gmail/Drive/Chat and turn them off. Go to Settings -> See all settings -> find under "Genera" the "Google Workspace smart features" -> turn smart feature setting off for both Google Workspace and all other Google products and hit save. (If you turned off the smart settings in your Gmail, it never hurts to open Drive and double-check that they're set to off there too.)
Quick Edit: I found the easiest way to get to the Smart Feature settings following the instructions above was to do it through Drive. Try that route first.