The Closed Beta / Nightly update 21.6.4 has been officially released for Redmi K40 / Mi 11X / POCO F3 (codename is alioth). Before updating, please make sure you have downloaded the exact ROM matching your Xiaomi phone/tablet. In Fastboot mode, you can check model code by typing
fastboot getvar product in cmd/shell.
Download Redmi k40 (alioth) China MIUI 12.5 21.6.4 Recovery ROM with Android 11.0. Firmware size is 3.8 GB.