As per Office 365 blog found here
Effective October 13th, 2020, Office 365 will only allow Office client connectivity from subscription clients (Office 365 ProPlus) or Office perpetual clients within mainstream support to connect to Office 365 services. (Please refer to the Microsoft support lifecycle site for Office mainstream support dates.)
Any Standalone Office 2016 will not connect to Office 365 services, such as Outlook, OneDrive for Business and Skype will not connect to Office 365 services.