If you are looking for the large gallery view of seeing up to 7 x 7 (49) videos, follow the steps to turn on the new meeting experience:

  1. Select your profile pic at the top of the Teams app, then Settings > General
  2. Select Turn on new meeting experience.
  3. Restart Teams desktop app. 

Note that this view is available when there are 10 or more attendees who are sharing video.

For more information, refer to https://techcommunity.microsoft.com/t5/microsoft-teams-blog/new-meeting-and-calling-experience-in-microsoft-teams/ba-p/1537581