Welcome Govind Atos-Bishat,
Thanks for reaching out to Microsoft Q&A Forum. I understand that Copilot is greyed out in classic Outlook on your Windows PC, while it works correctly in Outlook on the web and on your iPhone.
Could you confirm whether the greyed-out option is Copilot Chat, Draft with Copilot, or both? Also, is this a work or school Microsoft 365 account managed by your organization?
Please make sure you already tried the Q&A Assist steps. In addition, please try the following.
1, Check whether the issue occurs in your primary mailbox
- Open an email in your own primary mailbox and create a new email
- Check the Copilot option again
- Avoid testing from a shared, delegate, group, or archive mailbox
2, Update Microsoft 365 Apps.
- Open File > Office Account
- Under Update Options, select Update Now
- After the update finishes, close all Office applications and reopen Outlook
Looking forward to your update.