The "generally available" bit doesn't sound accurate. To activate it, you need to submit a "Request a trial" form.
For every other Google Workspace feature in GA, billing, subscriptions, and feature settings is available self-serve in Google Workspace Admin.
This is the first "generally available" feature I've seen that's still hidden behind a "request access" form after being called "generally available".
I'm pretty surprised that Google is breaking their own use of the "GA" terminology. General Availability has a pretty specific meaning to anyone who manages Google Workspace for a company, and the way they're rolling out Duet is not how they typically roll out new features.
Which leaves me wondering if this is more of a fluff piece. Has anyone actually gotten access to Duet yet?