Modern Document library: Search box gone?

I opened a support case with Microsoft and the support agent was bewildered as well. We gathered Screenshots and Fiddler logs. To my surprise today everything has reverted back to normal but only for classic team sites. On modern team sites I can still see the new searchbox but in modern document libraries the old searchbox at the top left has returned. At least it's working.

And we determined that this is a preview feature at the moment and only users that, in the M365 admin center under organizational profile, ar enabled for "Targeted release for selected users" will see that feature. I was relieved to learn that as only a few select of our users have gotten confused by that hiccup.

So for the most part, all good now. Thanks for chiming in.