Using Classic Outlook on Windows for personal email, calendar, and contact management
As someone else pointed out, this has been discussed and is in theory on the roadmap for July of this year. There were concerns on what it meant by Users Credentials but this was subsequently clarified to mean that the user must have an active 365 account in order to be able to access the shared mailbox and have been granted permissions (which is in fairness what you would expect)
(Current Microsoft Roadmap Microsoft 365 Roadmap | Microsoft 365)