Tonight, while working in Outlook (Office 365 Pro Plus) I switched on the Coming Soon toggle switch in the top right corner. Microsoft introduced the “Coming Soon” feature in 2018, I believe, and this Search change in November 2019. They are going live with it this month (Feb 2020) with Microsoft Search across the entire Microsoft 365 platform.
If you don’t already see it in Outlook, you can toggle the Coming Soon switch and it should be visible.
Once you restart Outlook, you should see the new location of the Search bar.
Ok, big deal, right? Well, it is nice because the Search bar will be in the same location across the Office 365 Pro Plus suite (Word, Excel, PowerPoint, Outlook, etc.). There are also some additional Actions that appear in the search results.
This will make it much easier to find and utilize the Search bar.
You can read more about the deployment here:
Just for reference, this is the version of Outlook I am running.