There's been a number of complaints in Xiaomi's user community about some of its recent phones and their proximity sensors. And it appears that the company has listened and has a plan to address those issues.
The exact root of the problem hasn't been confirmed, but it might have something to do with the new virtual proximity sensing. Perhaps that's why Xiaomi has decided to end its deal with Elliptic Labs - the OEM's supplier for the software that drives the virtual proximity sensing. It has now struck a deal with Minghao Sensing, although it's unclear when the new solution will make it to Xiaomi's phones.
In addition, the tech giant will try to fix these annoying bugs by seeding OTA updates to the affected devices in an attempt to re-calibrate the software.
We will see how this plays out, but it's good to see Xiaomi responding to the growing number of complaints about the proximity sensing issues.
Source (in Italian)
I have redmi 10 and when I call someone or attend the call screen goes black and doesn't turn on untill call cuts.
I have exactly the same issue on a brand new phone identical to yours. I just did a proximity sensor test and it fails.
An temp. fix is to press the lock button and resume your call while the phone is locked