There is no fix available, but you can always revert to an older version.

A new Microsoft-issued software patch for Outlook (Classic) on Windows 11 inadvertently broke encrypted email support - ...

You may see this error because the Microsoft 365 encryption service cannot verify your identity or check if you have permission to view the message. This is not ...

PCWorld reports that Microsoft has confirmed a bug in classic Outlook version 2511 preventing users from opening encrypted emails. This issue significantly impacts business users and organizations ...