Outlook Web Add-in Toolbar Icon Not Updating on Desktop App (Mac & Windows)

Question

I have developed a custom Outlook Web Add-in and installed it in the Outlook desktop app (Mac & Windows) using a custom XML manifest file for all my employees. The add-in includes a toolbar button with a custom icon.

After updating the icon URL in the manifest and reinstalling the add-in, the updated icon appears correctly in the browser version of Outlook, but in the desktop app (Mac & Windows), the old icon is still displayed.

I tried following things

1. Updated the manifest file with the new icon URL.
2. Uninstalled and reinstalled the add-in using the updated manifest.
3. Cleared the cache:
4. Restarted Outlook.

I tried everything but nothing worked. Apart from the toolbar icon everything is getting updated