Hi, I'm Diane and I'm happy to help you today.
If you see it in the other apps, you are signed into OneDrive, so its not that.
Did you Quit and restart Outlook?
Are you in the mailbox that has the copilot subscription? It is only available in that mailbox, not other accounts in your profile.
This is Microsoft article on using Copilot in email:
https://support.microsoft.com/office/draft-an-email-message-with-copilot-in-outlook-3eb1d053-89b8-491c-8a6e-746015238d9b#OSVersion=macOS
Let me know how it goes, I'm here to help you further if needed.
-- Diane