There may be the following reasons for the lag when Xiaomi TV screen is projected.
1. If you are using a third-party screen mirroring software, there may be a problem with the software. You can disconnect and reconnect, or use other screencasting software.
2. There may be a problem with your network. If your network signal is weak, the signal will be unstable when you cast the screen, and there will be lags. Please check if your network has a stable signal.
3. It may be because your Mi TV is out of memory. If your TV has too many apps installed, but Xiaomi TV has less memory. Then there will be lag when you cast the screen. Please reduce your TV's apps and clear your TV's memory.