I've created a guide and composed a pack for ZTE Nubia 17 mini to unlock bootloader and install TWRP recovery then grant root access.
It can be also used for Z17 (not mini) with some minor modifications.
Happy 'hacking' !
EDIT: Reports arrived on 'bootloader locked' screen not showing. Reports also came on successful process - after error encountered by the script - by continuing the steps of the guide.