The ability to pin emails in Outlook may vary based on the version you are using. In some cases, features like pinning may not be available or may have been removed in updates. If you can still flag emails but not pin them, it could be due to changes in the application's functionality or user interface. Additionally, if you cannot see the pin symbol on previously pinned emails, it might indicate that the feature is no longer supported in your current version of Outlook.
To resolve this issue, you can check for updates to your Outlook application, as functionality can change with new releases. If the problem persists, consider reaching out to Microsoft support for further assistance regarding the specific features available in your version of Outlook.