It’s expected that your Xiaomi phone screen light should turn off when you are making a phone call so that your skin will not be touching your device and operating it. So if your Xiaomi device screen is not off then it’s possible that you have accidentally enabled some function as the speaker.
To fix these issues, we need to activate the proximity sensor, which darkens or turns off the screen during a phone call. However, you should note that this feature is not available on all Xiaomi Redmi or Poco phones.
How to Turn Off/On Proximity Sensor on Xiaomi, Redmi, and Poco Phones
Step 1: Open the Phone App.
Step 2: Open the Setting.
Step 3: Next tap on the incoming calls.
Step 4: Now you can Enable or Disable proximity sensor.
That’s how you can enable proximity sensors on your Xiaomi phone.