Hi AhmadRashid-8680!
I am afraid to tell you that your idea is not available in Microsoft Teams.
To my knowledge, you can only control who can turn on the video in the meeting and who cannot by assigning meeting policy to each user. For more details, you can refer to:
https://learn.microsoft.com/en-us/microsoftteams/meeting-policies-in-teams#allow-ip-video
If the above cannot meet your requirements, we recommend you that please give a feedback to Teams UserVoice(Link: https://microsoftteams.uservoice.com/forums/555103-public/suggestions/40623253-teacher-to-view-video-feeds-of-at-least-20-student). Microsoft will always focus on customer’s feedback and experience. Some new features would be added to the services based on customers' feedback in the future, and your good ideas will be very helpful for them to improve the service.