I tried to unblock it, it did not work out, I could not flash it either, according to the instructions on the site (
Xiaomi Mi Mix 2S - MIUI firmware (Post Camerado # 73629162)looked (loader locked) ...
It helped to delete all data (as far as I remember in Wipe all data recovery), before that the phone went to Recovery and an endless bootlap, it was possible to transfer to Fastboot. At the moment, the body with a locked bootloader (version 8/256), is working, I decided not to do unlock yet.