As of today, Application Guard for Office is now generally available.

Files from the internet and other potentially unsafe locations can contain viruses, worms, or other kinds of malware that can harm your users’ computer and data. To help protect your users, Office opens files from potentially unsafe locations in Application Guard, a secure container that’s isolated from the device through hardware-based virtualization. When Office opens files in Application Guard, users can securely read, edit, print, and save those files without having to re-open files outside the container. This feature will be off by default.

Here is the installation guide to get started:
Application Guard for Office 365 for admins – Office 365 | Microsoft Docs

Customers will receive a Message center post on Wednesday, 1/27/2021. Microsoft 365 Roadmap Featured ID is 67101. Application Guard for Office is only available to organizations with a Microsoft 365 E5 or Microsoft 365 E5 Security license.