Using classic Outlook for Windows in business environments
Dear DionneParks,
Welcome to Microsoft Community.
I understand that you can use Copilot in Office applications like Word, Excel, but not in Outlook.
I'll be happy to help you, it depends on the type of account you log in to Outlook, for individual users, only use the Microsoft domain name (@hotmail.com @live.com @outlook.com @msn.com etc.) supports Copilot, and if your email address is a third-party domain, this feature isn't available at this time.
How to find and enable missing Copilot button in Microsoft 365 apps - Microsoft Support
You can try adding an @outlook.com alias to your account, then add this address in Outlook, and then click "File – Office Account – Switch account" to switch to the new @outlook.com address.
After restarting Outlook, you can see if you can enable Copilot, and if not, then the reason is that the account you used for the subscription is a third-party email address.
Feel free to post back if you have any progress with that.
Best Regards,
Jason.YA - MSFT | Microsoft Community Support Specialist