If you have bootloop issue after install update, then follow this steps in this order:
1. Install latest TWRP recovery (if you already have it then skip this step)
2. Boot to TWRP recovery and stay in TWRP recovery until the last step
3. Wipe > Advanced Wipe: Wipe Dalvik/ART Cache, Wipe Cache, Wipe System
4. Wipe > Format Data (It formats the following partitions: Data, Internal Storage)
5. Reboot to TWRP Recovery
*6. Connect Phone to PC while you are in recovery and copy latest xiaomi.eu ROM.zip to internal storage and then Install ROM
7. Reboot to System
*You can use USB-OTG pendrive or ADB Sideload installation method too as alternative solution to install ROM.zip
Once you have done this then you will never ever have any issue with further updates. Just install further updates via updater app, no any additional action needed.
Thank you for the tip. I was wondering. I read that you should never format /system on any Xiaomi phone. It is safe for the Mi Mix 2? How do I know which phones it is safe for and which ones it isn't?