Neufbox6, openwrt 23, need help for flash

[sms]

hello

im trying to install latest release of openwrt (23)
using the following file :
https://downloads.openwrt.org/releases/23.05.0/targets/bcm63xx/generic/openwrt-23.05.0-bcm63xx-generic-sfr_neufbox-6-sercomm-r0-squashfs-cfe.bin

i well renamed my openwrt-23.05.0-bcm63xx-generic-sfr_neufbox-6-sercomm-r0-squashfs-cfe.bin into /tftpboot/bcm963xx_fs_kernel

unfortunately, using download mode, im stopped by error 21 :

CFE> HELO
CPUI
L1CI
HELO
CPUI
L1CI
DRAM

PHYS
STRF
400H
PHYE
DDR2
SIZ4
SIZ3
SIZ2
DINT
USYN
LSYN
MFAS
LMBE
RACE
PASS

ZBSS
CODE
DATA
L12F
MAIN
NAN0
BT01
0001
NAN9
BT01
0992
NAN9
NAN3
RFS2
NAN5

CFE version 1.0.38-112.70 for BCM963268 (32bit,SP,BE)
Build Date: Fri Oct 18 19:11:22 CEST 2013 (gmu@gmu-thinkpad)
Copyright (C) 2000-2011 Broadcom Corporation.

boot...
** tftpboot requested
NAND flash device: name ST NAND512W3A2CN6, id 0x2076 block 16KB size 65536KB
RTL: chip 6000.1000 probed
TX/RX delay set on switch side!
Chip ID: BCM63168D0, MIPS: 400MHz, DDR: 400MHz, Bus: 200MHz
Main Thread: TP0
Memory Test Passed
Total Memory: 134217728 bytes (128MB)
Boot Address: 0xb8000000

Board IP address : 192.168.22.22:ffffff00
Host IP address : 192.168.22.68
Gateway IP address :
Run from flash/host (f/h) : f
Default host run file name : vmlinux
Default host flash file name : bcm963xx_fs_kernel
Boot delay (0-9 seconds) : 1
Boot image (0=latest, 1=previous) : 0
Board Id (0-13) : NB6V-SER-r0
Number of MAC Addresses (1-32) : 11
Base MAC Address : 24:95:04:e7:05:e8
PSI Size (1-64) KBytes : 24
Enable Backup PSI [0|1] : 0
System Log Size (0-256) KBytes : 0
Main Thread Number [0|1] : 0

DHCP request failed on device eth0: CFE error -21
Disabling Switch ports.
Flushing Receive Buffers...
0 buffers found.
Closing DMA Channels.

how could it be fixed ?
there is no classic "f" command to just gather image from tftp+boot. However, looks like lot of people failed to install it on, even if wifi 2.4 in 802.11g is supported (highly enough here) :

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(whom normally just push the front button might successfully download the firmware..)

before today, i tried another attempt :

Illegal whole flash image

Retry loading it as a compressed image.
Code Address: 0xFFFFFFFF, Entry Address: 0xffffffff
Failed on decompression. Corrupted image?

thanks for helping!