B2B Collaboration vs B2B Direct Connect --- Shared Channels

We have several agencies/partners we collaborate with heavily, and we're struggling to find the best way to accomplish ongoing, sustainable tenant-to-tenant relationships.

We remain quite confused by B2B Collaboration vs. B2B Direct Connect - especially as the two relate to Shared Channels in Teams. My current understanding is that B2B Direct Connect is **only** functional at this time for use with Shared Channels in Teams.

We *thought* we'd potentially like to configure Direct Connect relationships to avoid the need for large numbers of guest accounts within our own tenant, for use with Shared Channels. In doing initial testing between two of the tenants (one a GCC, the other a standard/commercial), we've done the following:

• configured the cloud & other settings in both tenants, each adding the other as an organization in the Cross-Tenant Access Settings, and modifying the Microsoft Cloud Settings to include "Microsoft Azure Government" 
• tried to add one of the "connected tenant" users as a member of a Shared Channel

When sharing a Shared Channel "with people" - and then typing in the email address of the "Direct Connect" user from the other tenant - it's obvious that some directory sharing is happening as the email address is resolved to the correct username from the other tenant; however when trying to complete the share, we end up with, "Something went wrong. You can't share channels with orgs in this environment."

This article (Cross-tenant access overview - Microsoft Entra | Microsoft Learn) has a note that "B2B direct connect is not supported for collaboration with Azure AD tenants in a different Microsoft cloud" although I can't find a reference anywhere to the specific message above - so I want to be absolutely sure before we abandon the "Direct Connect" idea.

Can anyone confirm that "B2B Direct Connect" is, indeed, **not possible** between a GCC tenant and a standard/commercial tenant?