https://linuxfr.org/news/installer-lineageos-sur-son-appareil-android
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i think you can find the solution to your problems with the fastboot command-lines describes in the superman’s how-to, in french :
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Boot to your Stock-ROM,
in the dev options, enable ADB debuging,
reboot the device in “bootloader” mode by typing :
adb reboot bootloader
Check if the device is reconised by the PC :
fastboot devices
if it ils good, type :
fastboot oem unlock
fastboot flashing unlock
Then reboot the device by :
fastboot reboot
return to the dev options and re-enable “ADB debugging” and “OEM unlock” if you find it.
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