Exclusive: Your Xiaomi phone won't get HyperOS updates if you unlock the bootloader
www.androidauthority.com
Xiaomi has confirmed to Android Authority that its HyperOS phones will not receive updates if their bootloader is unlocked. Read on for more!

Seems like Xiaomi is heavily clamping down on bootloader unlocking in China. Global versions also have a new restriction: no updates without locked bootloader.