Classic Outlook (Microsoft 365): copilot button stays gray

I don’t know which license you are using. Normally, when this happens, the Outlook add-on is not loading correctly or the license is not valid to use Copilot, or your Copilot credits (Office Family) have ended.
If your license is fine, try opening Outlook Web and Classic at the same time and test Copilot in both, then compare the behavior. If Copilot in Outlook Web does not work, there is likely a problem with your license (I suggest opening a ticket with Microsoft).
If the problem still occurs, I recommend reinstalling Outlook (this tip is useful if you are in a rush), because if the issue is temporary, Classic Outlook may fix itself