Unfortunately this Xiaomi phone has a very annoying procedure to unlock the bootloader: it is mandatory to execute an on-line procedure using a PC running an MS-Windows program, on the phone you have to enable the mobile internet connection (thus requiring a valid SIM card) and execute an app which will collect several data from the phone (IMEI, etc.). Once you start the procedure, you will be granted the right to unlock the bootloader, but with a wait time of several days. In my case the delay was about 14 days.

At the first run - once added a Google account and activated a WiFi connection - the phone suggested to update the operating system; the proposed update was MIUI V10.2.6.0.OCGMIXM Stabile 638 Mb. The upgrade failed: the download phase was plagued by error messages like L'app Google continua a interrompersi (Google App Keeps Stopping) and similar messages from other apps. Once downloaded the upadte, the phone rebooted. On the black screen there was the message Aggiornamento MIUI in corso, non riavviare il dispositivo, then an error message informed that the upgrade failed. The phone rebooted and a popup informed that the upgrade failed, suggesting to retry the ROM download.