My screen phone always dark when incoming call

Hi Morhi,

Generally the problem you're seeing tends to be caused by a faulty proximity sensor. The sensor is supposed to detect when you're on a call and put the phone up to your face and then blank the screen. When you take your phone away from your face, it's supposed to detect that and light the screen back up.

However, when the sensor is defective, it will always say that your face is next to the phone and continually blank the screen whenever you're on a call. You may be able to work around that by putting the phone in speakerphone mode which will usually ignore the proximity sensor.

Of course you'll want to try as many software solutions as you can, such as starting the phone in safe mode, doing a hard reset, and perhaps even doing a wipe and restore of the phone's software (be sure to back up first). Ultimately, if none of that helps, then it's likely you have a failed sensor which will need to be replaced.

Although I wasn't able to locate a guide specifically for the Note 8, there's one for the Note 8 Pro that appears to be similar enough that it should get you through the process of replacing the proximity sensor on your phone.

Manuales / Xiaomi Redmi Note 8 Pro / Proximity sensor

The part itself shouldn't be too hard to find; I usually start with places like Amazon, eBay and AliExpress, but here's one that came up on a cursory search I did that should work.

Proximity Distance Ambient Flash Light Sensor Flex Cable For Xiaomi Redmi Note 8 Pro 9T 9 Pro 9s 10X

That's the first thing I would try after exhausting all of the software possibilities. Let us know what you find and if that does the job for you; success stories are appreciated and we can always learn something when things don't go right.