Using New Outlook on Windows for personal email, calendar, and contact management
Microsoft 365 Basic doesn't include the desktop version of Office apps, which include Word, Excel, PowerPoint, Classic Outlook, and premium features of New Outlook.
If you want to use Classic Outlook you need at least the Msft 365 Personal subscription.
But you should be still able to use the free New Outlook. Is this new error happening with New Outlook?