Microsoft has announced the availability of the visual update.

Previously, Microsoft made the visual upgrade automatically available to 50% of subscription customers running Current Channel versions and users of Microsoft Office Home & Student 2021, Microsoft Office Home & Business 2021, Microsoft Office Professional 2021, and Microsoft Office Personal 2021.
The visual refresh can be easily switched off or on by tapping the Coming Soon button in the top right corner of the app. Simply click the megaphone icon in Word, Excel, PowerPoint, or OneNote to open the Coming Soon window, learn more about the visual refresh changes, and use the toggle to switch between the new and current interfaces, and apply the setting to all Office programs.

The office theme and the quick access toolbar are two noticeable modifications. The Office now defaults to matching your Windows theme, and all themes have been updated. Users can experience the visual refresh in their preferred Office theme, such as black (with Word Dark Mode enabled), white, colorful, or dark grey.
On the other hand, the quick access toolbar is now hidden by default to simplify your interface. To re-display it, right-click the ribbon or select the Ribbon Display Options icon, then select Show Quick Access Toolbar.
For select Current Channel customers using Windows 10 version 2110 and build 14527.20226 or later, this visual update became available automatically.

If you don’t see the update, Microsoft says you’ll need to restart any Office software to get the visual refresh. Otherwise, if you do not see the megaphone icon in the top right corner (as described above), the update is not yet accessible to you. If you’re on Windows 11, you can get the update, but you’ll need to restart any Office software to get the visual refresh.
Source: Microsoft