Dear Dilip H,
Greetings! Thank you for posting in the Microsoft forum.
May I know if right clicking the file and selecting Unpin from list did any trick? If you’ve tried this, then try clicking the pin button again to unpin the file.

If it still didn’t work, please provide us with the following information, so we can find the related information:
- Please provide the screenshot of Microsoft 365 Product Information. To get this screenshot, open OneNote on your system, click File>Account, capture the screenshot of all the information mentioned under Product Information.
- Does this happen only in PowerPoint app?
We will look forward to your reply. Stay safe and stay healthy.
Sincerely,
Neha Singh | Microsoft Community Moderator