My Solution for the "clean all and lock" Problem -> go to s-unlock.com and register. To unbrick my brandnew Mi 8 cost me $ 36,00 and it worked perfectly. But you have to open your phone, as Marcio mentioned above, to set it into EDL mode. Response time is very short and it was all done with Teamviewer.
Woud be interesting to know who is behind this unlocking service - freelance hackers who found a backdoor, or Xiaomi service center employees who found a lucrative source of extra income.
And why have all these posts recommending and linking to a shadowy pay-for site not been deleted as spam by a moderator?