@advocatux your proposed links answer my question
Ubports is a great work many thanks to all !

The "Could not flash core_nhlos_b partition" error often means you're trying to flash a critical partition in standard
fastboot mode on a locked bootloader...

But :

$ fastboot flashing unlock
< waiting for any device >
FAILED (remote: ' Device already : unlocked!')
fastboot: error: Command failed

???

Please help

Well !

I changed the USB-cable and now it's OK

Many thanks for your works and making smartphone free !

SOLVED !