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:
- Select your profile pic at the top of the Teams app, then Settings > General.
- Select Turn on new meeting experience.
- 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