Unable to finish /e/ installation on Samsung Galaxy S8

[piero]

…IT IS THE CRUTIAL STEP !..

@piero

• immediately Boot to Recovery before any other boot mode attempt,
  hold Volume up + Home + Power.
  release when you see the very little blue line in the bottom of the screen…

You must see the TWRP flash logo,

and the welcome screen :

if you see something like that :

It FAILED, this is the Official Stock Vendor Samsung / Gogol Firmware Recovery screen !
Please re-read and retry the flashing process of TWRP.