Support update for Business Connectivity Services in Microsoft 365

Hi josharistocrat, I'm sorry to hear that this announcement was a surprise.  Different product teams may have slightly different processes, but feature retirements in Microsoft 365 are typically communicated to customers in the following ways:

1. Announcements to the Microsoft 365 Message Center.  Tenant administrators can find the M365 Message Center in the M365 Admin Center.  It's regularly updated with important announcements about the M365 service and the specific features your particular tenant is using.  For example, the Business Connectivity Services (BCS) retirement announcement was published in the M365 Message Center back in October 2023 as Message Center post MC679737.
2. Feature documentation.  Microsoft will update relevant feature documentation articles about upcoming feature retirements.  For example, the following feature documentation articles were either added or updated to announce the upcoming retirement of Business Connectivity Services:
   1. Business Connectivity Services (BCS) retirement in Microsoft 365
   2. Manage Business Connectivity Service Applications
3. Product team blogs.  Many M365 product teams maintain their own blogs to share announcements, including the SharePoint team.  The SharePoint team will post important retirement announcements to its blog, including this announcement.  Other recent examples include:
   1. Remote Event Receivers retirement update in SharePoint Online
   2. Azure ACS retirement in Microsoft 365
   3. SharePoint Add-In retirement in Microsoft 365
   4. Support update for InfoPath Forms Services in Microsoft 365
   5. Support update for SharePoint 2013 workflow in Microsoft 365

I hope this helps to make it easier to find retirement announcements in the future.