In order to use the Large Gallery view in Microsoft Teams, you must first enable the new meeting experience.
1. Open Microsoft Teams
2. Click your Profile Icon in the top right corner of the screen then click Settings.
3. Enable the Turn on New Meeting Experience option, then click the Close button in the top right corner of the settings window.
4. From the system tray, click the up arrow then right click on the Microsoft Teams icon.
Hint: The System Tray is found in the bottom right corner of your screen near the date and time.
5. Click Quit
6. Open the Microsoft Teams application again.
(You will find the Microsoft Teams icon in your Start Menu, or in most instances on your desktop as a shortcut)
7. Once within a teams call, click the three dots to open the more options menu, then click Large Gallery.
Note: the Large Gallery view will be unavailable if there are not enough participants in the call.