Generally, you can install Youtube directly on your Xiaomi Box. If you can find the app store on your Xiaomi Box, you can follow the below method to install Youtube to Mi Box.
1. Navigate to the home screen of the Xiaomi Mi Box.
2. Open the Google Play Store app.
3. Search for YouTube. then select the YouTube app and open it.
4. You can find the Install button. Click the button to download YouTube and install it on your MI Box.