Solution:
First of all, please make sure to use the correct cable to connect to Xiaomi TV and set-top box, and make sure that it is connected to the correct interface. HDMI can be directly connected to the TV's HDMI interface. The AV interface should also correspond to the red, white and yellow colors one by one. After connecting the cables, please also enter the TV's signal source interface, replace the TV's signal source with the corresponding HDMI interface or AV interface, you can enter the set-top box interface. If you have any questions, please contact Xiaomi after-sales team in time.
Does it help?