Hi!
I'm sorry to hear that you're having trouble screencasting/mirroring your Redmi Note 11 to an Android TV. This can be frustrating, especially when you need to use it for your class presentations.
There are a few things you can try to fix this issue:
1. Make sure both your Redmi Note 11 and your Android TV are connected to the same Wi-Fi network.
2. Check if your Android TV is compatible with Google Cast or Miracast. These are two popular screen mirroring technologies that allow you to cast your phone's screen to your TV wirelessly.
3. On your Redmi Note 11, go to Settings > Display > Cast screen. Make sure that the toggle switch is turned on.
4. If your Android TV supports Miracast, you can try using the Miracast app on your Redmi Note 11 to cast your screen to your TV. You can download this app from the Google Play Store.
5. If all else fails, you can try using a third-party screen mirroring app such as AllCast or AirScreen.
I hope these tips help you fix the issue and allow you to screencast/mirror your Redmi Note 11 to your Android TV successfully. Let me know if you have any further questions or concerns.