The Files tab in channels is now "Shared"

I've found this Roadmap article about this feature: https://www.microsoft.com/en-us/microsoft-365/roadmap?id=470597

The Microsoft 365 Admin Message Center Message ID MC1025217 says "Before rollout, we will update this post with new documentation."

But I can't find any documentation and users in my organisation have this new feature. It's not in any of the blog posts here.
Any thoughts on where to find useful end user materials?