The manufacturer announced this on the official forum, but do not rush to rejoice. The point is that the firmware will not be distributed over the air. You will have to install it yourself via Fastboot and the Xiaomi Mi Flash Tool. Thus, Xiaomi decided to protect itself, because according to the company, the system does not work very smoothly and there are errors in it.
MIUI 12 can only be installed by smartphone owners in China so far. It is not known whether such an opportunity will appear for users of global versions of devices.
As a reminder, Redmi 6 and Redmi 6A came out in 2018. Now the devices run on the Android 9 operating system, on top of which the MIUI 11 shell is installed.