¡¡¡ALELUYA!! OK, problem solved:
What I did was to install “twrp 3.0.2-0-libra” via Play Store (as recommended in TS WEB), and … voilà!, twrp working perfectly alright!
Then, I flashed to rom 6.12.22, where my Mi4C belongs to, and … from which, should have never changed.
Thanks Iamme729 for...