[General Questions and Answers] m2m4m5:
updated instructions

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install ReiBoot-for-Android-2.0.0.15 (on PC)

>>> and run it once (or at least fastboot will not work without other help)

extract platform-tools_r28.0.3-windows.zip somewhere

rename the folder to adb and place it in C:\

extract Gome_2017M27A_MT6757_V01_20180122.zip somewhere

(and delete the Gome_2017M27A-folder later to save space)

copy folder Firmware to C:\adb and rename it to stock

now you have the original-images in C:\adb\stock

create a folder C:\adb\twrp

and extract Gome_U7_3.2.3.rar in it

create folder C:\adb\2017

place these files there:

Magisk-v19.2.zip

no-verity-opt-encrypt-6.0.zip

MagiskManager-v7.2.0.apk

Root_Essentials_v2.4.9.apk

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now you can start your phone for the first time (if it's new)

what you choose now is not so important because it gets deleted later

go to settings >>> about phone >>> push build-number 7 times >>> makes developer-options available >>> go back

settings >>> developer-options >>> activate oem-bootloader-unlock and usb-debugging

connect phone-usb-cable to pc

on pc >>> in menu >>> windows-system >>> right-click on shell >>> more >>> run as admin [maybe not]

go to platform-tools-folder (C:\adb) (for example with cd\adb)

>>> type: adb devices >>> no device found [maybe]

confirm/allow the connection on phone (permanently)

>>> type: adb devices >>> phone found (shows serial)

>>> type: adb reboot bootloader

phone boots in fastboot-mode [small writing in left down corner in phone display]

on pc in shell >>> type: fastboot flashing unlock

>>> push (volume-)up-bottom on phone to confirm

on pc in shell >>> type: fastboot flash boot twrp\boot.img

--- DO NOT FLASH THE RECOVERY-IMAGE NOW ---

on pc in shell >>> type: fastboot reboot

message -- ERASING -- appears

and phone boots again

phone boots and GOME-logo stays

>>> wait until phone is newly initialised, which takes 5 minutes, and let it start

this time choose what you really want (name, ...) / setup your phone properly

make developer-options and usb-debugging available again

(you can verify it again with: adb devices)

on pc in shell >>> type: adb push 2017 /sdcard

on pc in shell >>> type: adb reboot bootloader

on pc in shell >>> type: fastboot flash recovery twrp\recovery.img

on pc in shell >>> type: fastboot reboot

now go into recovery-mode

>>> for this use ReiBoot on PC

>>> or press and hold the power-button on the phone

and (then at the same time) the (volume-)up-button

until a menue appears,

release then first the power-button

and then the (volume-)up-button,

select what you want there with the (volume-)up-button

and press then the (volume-)down-button to confirm it

phone reboots to TWRP-recovery

right grey button, scroll up, choose english, ok

(maybe mark never show this question again)

slide blue-white arrow on bottom to right

in TWRP-recovery choose Install (left upper corner)

choose Magisk-v19.2.zip from /sdcard/2017

add more zips

choose no-verity-opt-encrypt-6.0.zip

mark reboot after installation

slide blue-white arrow on bottom to right

phone reboots (normally)

>>> ROOT <<<

(without magisk-app)

(and you don't need to format anything anywhere)

you can install and run RootEssentials now

it appears a super-user-request >>> grant

in tools >>> scroll down >>> root-checker

message: root-privileges found

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if your phone endlessly loops to TWRP-recovery

you have flashed the modified-boot-image

and the modified-recovery-image at the same time

solution: flash the stock-recovery-image again

then the -- ERASING -- message appears

and the phone boots normally after that to GOME

you can now flash the modified-recovery-image again

and try to get everything working

but it's better to flash both stock-images again

and give it a completely new start

(maybe even uninstall Magisk with a zip-file)

(and lock it again temporarely)

if not, the Root-Essentials-App (and others)

maybe work only with the Magisk-Manager-App installed

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if the phone boots to TWRP-recovery

and wants to decrypt data you have done something wrong

maybe you shouldn't erase the filesystem now,

but after all this is not really important

this could help: (inside twrp-recovery)

>>> push reboot and select bootloader

>>> phone reboots to fastboot-mode

on pc in shell >>> type: fastboot flash recovery stock\recovery.img

on pc in shell >>> type: fastboot flash boot stock\boot.img

on pc in shell >>> type: fastboot reboot

and start new from beginning

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if you copy apk-files from your pc to your phone

with the adb-push-command and a message appears

that the file-format of the files is not supported

if you try to install them on your phone

simply change the name of the folder (on your phone)

in which the apk-files are stored

and (temporalely) everything works again fine