What is unclear to you?
DO NOT try to lock the bootloader unless you have an official Chinese ROM installed. Otherwise, you will brick your phone. (you will destroy it, you will have to seek service)
If you use any ROM other than the official Chinese one, you will need to root and perform the...
You can't do that, otherwise you'll brick your phone.
Attention!
You can only lock the bootloader in the following cases:
- CN devices with CN ROM
- Global devices with any Global ROM derivative (MI, EEA, RU, TU, TW, ID, IN, etc.)
TWRP is not required.
xiaomi.eu is a hybrid ROM, it can be installed via fastboot or TWRP.
See the first post of this thread or this tutorial: https://xiaomi.eu/community/threads/how-to-install-xiaomi-eu-rom-for-devices-a-b.62738/post-624043
I would like to point out that the situation with GPay and some applications requiring greater security is currently problematic.
https://xiaomi.eu/community/threads/regarding-google-play-integrity-google-pay-wallet.75761/post-748452
If you are not Chinese with a Chinese ID and a Chinese Xiaomi account, this is not possible.
If we are talking about the Chinese version of the device.
"For Global devices, the bootloader can be unlocked"
It doesn't matter, because if you are switching from an official ROM to a xiaomi.eu custom ROM, a clean installation is required.
- You can directly install xiaomi.eu ROM https://xiaomi.eu/community/threads/how-to-install-xiaomi-eu-rom-for-devices-a-b.62738/post-624043
- After installation You...