After following instructions to Turn Office 365 Bookings on in the following article, we've lost RingCentral Desktop App's ability to connect to Microsoft Outlook 365 calendar and Contacts.
https://learn.microsoft.com/en-us/microsoft-365/bookings/turn-bookings-on-or-off?view=o365-worldwide
Exchange Online Powershell Commands Entered before Issue started occurring (conf ver).pdf