So finally success, luci is back 
(IPQ40xx) # setenv serverip 192.168.1.64
(IPQ40xx) # setenv ipaddr 192.168.1.1
(IPQ40xx) # set fdt_high 0x85000000
(IPQ40xx) # tftp openwrt-23.05.3-ipq40xx-generic-zte_mf286d-initramfs-zImage.itb
MAC0 addr:0:3:7f:ba:db:ad
PHY ID1: 0x4d
PHY ID2: 0xd0b1
ipq40xx_ess_sw_init done
eth0
eth0 PHY0 Down Speed :10 Half duplex
eth0 PHY1 Down Speed :10 Half duplex
eth0 PHY2 Down Speed :10 Half duplex
eth0 PHY3 up Speed :1000 Full duplex
eth0 PHY4 Down Speed :10 Half duplex
Using eth0 device
TFTP from server 192.168.1.64; our IP address is 192.168.1.1
Filename 'openwrt-23.05.3-ipq40xx-generic-zte_mf286d-initramfs-zImage.itb'.
Load address: 0x84000000
Loading: #################################################################
#################################################################
#################################################################
#################################################################
#################################################################
#################################################################
###############################################################
done
Bytes transferred = 6639048 (654dc8 hex)
(IPQ40xx) # bootm $loadaddr
## Booting kernel from FIT Image at 84000000 ...
Using 'config@ap.dk04.1-c1' configuration
Trying 'kernel-1' kernel subimage
Description: ARM OpenWrt Linux-5.15.150
...
tarting kernel ...
[ 0.000000] Booting Linux on physical CPU 0x0
[ 0.000000] Linux version 5.15.150 (builder@buildhost) (arm-openwrt-linux-muslgnueabi-gcc (OpenWrt GCC 12.3.0 r23809-234f1a2efa) 12.3.0, GNU ld (GNU Binutils) 24
[ 0.000000] CPU: ARMv7 Processor [410fc075] revision 5 (ARMv7), cr=10c5387d
[ 0.000000] CPU: div instructions available: patching division code
[ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[ 0.000000] OF: fdt: Machine model: ZTE MF286D
...
[ 27.350814] qca8k-ipq4019 c000000.switch wan: configuring for phy/psgmii link mode
[ 31.437364] qca8k-ipq4019 c000000.switch lan2: Link is Up - 1Gbps/Full - flow control rx/tx
[ 31.437458] br-lan: port 1(lan2) entered blocking state
[ 31.444547] br-lan: port 1(lan2) entered forwarding state
[ 31.450458] IPv6: ADDRCONF(NETDEV_CHANGE): br-lan: link becomes ready
...
BusyBox v1.36.1 (2024-03-22 22:09:42 UTC) built-in shell (ash)
_______ ________ __
| |.-----.-----.-----.| | | |.----.| |_
| - || _ | -__| || | | || _|| _|
|_______|| __|_____|__|__||________||__| |____|
|__| W I R E L E S S F R E E D O M
-----------------------------------------------------
OpenWrt 23.05.3, r23809-234f1a2efa
root@OpenWrt:/# ifconfig br-lan
br-lan Link encap:Ethernet HWaddr 10:3C:59:B0:67:B7
inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0
...
linux:~ # scp -p /srv/tftpboot/openwrt-23.05.3-ipq40xx-generic-zte_mf286d-squashfs-sysupgrade.bin 192.168.1.1:/tmp
root@OpenWrt:/# ls -l /tmp/open*
-rw-r--r-- 1 root root 7025211 Apr 23 2024 /tmp/openwrt-23.05.3-ipq40xx-generic-zte_mf286d-squashfs-sysupgrade.bin
root@OpenWrt:/# mtd erase rootfs
Unlocking rootfs ...
Erasing rootfs ...
root@OpenWrt:/# sysupgrade -n /tmp/openwrt-23.05.3-ipq40xx-generic-zte_mf286d-sq
uashfs-sysupgrade.bin
[ 445.118553] ubi0: attaching mtd9
[ 445.293043] ubi0: scanning is finished
[ 445.293090] ubi0: empty MTD device detected
[ 445.316356] ubi0: attached mtd9 (name "rootfs", size 29 MiB)
[ 445.316413] ubi0: PEB size: 131072 bytes (128 KiB), LEB size: 126976 bytes
[ 445.321107] ubi0: min./max. I/O unit sizes: 2048/2048, sub-page size 2048
[ 445.327824] ubi0: VID header offset: 2048 (aligned 2048), data offset: 4096
[ 445.334649] ubi0: good PEBs: 232, bad PEBs: 0, corrupted PEBs: 0
[ 445.341440] ubi0: user volume: 0, internal volumes: 1, max. volumes count: 128
[ 445.347687] ubi0: max/mean erase counter: 0/0, WL threshold: 4096, image sequence number: 2690910022
[ 445.354705] ubi0: available PEBs: 208, total reserved PEBs: 24, PEBs reserved for bad PEB handling: 20
[ 445.364348] ubi0: background thread "ubi_bgt0d" started, PID 2513
UBI device number 0, total 232 LEBs (29458432 bytes, 28.0 MiB), available 208 LEBs (26411008 bytes, 25.1 MiB), LEB size 126976 bytes (124.0 KiB)
Fri Mar 22 22:17:00 UTC 2024 upgrade: Commencing upgrade. Closing all shell sessions.
[ 445.833521] ubi: mtd9 is already attached to ubi0
Watchdog handover: fd=3
- watchdog -
Watchdog did not previously reset the system
Fri Mar 22 22:17:01 UTC 2024 upgrade: Sending TERM to remaining processes ...
Fri Mar 22 22:17:05 UTC 2024 upgrade: Sending KILL to remaining processes ...
[ 456.440030] stage2 (2580): drop_caches: 3
Fri Mar 22 22:17:11 UTC 2024 upgrade: Switching to ramdisk...
Fri Mar 22 22:17:13 UTC 2024 upgrade: Performing system upgrade...
verifying sysupgrade tar file integrity
Volume ID 0, size 24 LEBs (3047424 bytes, 2.9 MiB), LEB size 126976 bytes (124.0 KiB), dynamic, name "kernel", alignment 1
Volume ID 1, size 32 LEBs (4063232 bytes, 3.8 MiB), LEB size 126976 bytes (124.0 KiB), dynamic, name "rootfs", alignment 1
Set volume size to 19300352
Volume ID 2, size 152 LEBs (19300352 bytes, 18.4 MiB), LEB size 126976 bytes (124.0 KiB), dynamic, name "rootfs_data", alignment 1
sysupgrade successful
umount: can't unmount /dev: Resource busy
umount: can't unmount /tmp: Resource busy[ 461.874454] reboot: Restarting system
...
...
...
Starting kernel ...
[ 0.000000] Booting Linux on physical CPU 0x0
[ 0.000000] Linux version 5.15.150 (builder@buildhost) (arm-openwrt-linux-muslgnueabi-gcc (OpenWrt GCC 12.3.0 r23809-234f1a2efa) 12.3.0, GNU ld (GNU Binutils) 24
[ 0.000000] CPU: ARMv7 Processor [410fc075] revision 5 (ARMv7), cr=10c5387d
[ 0.000000] CPU: div instructions available: patching division code
[ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[ 0.000000] OF: fdt: Machine model: ZTE MF286D
...
[ 53.997755] br-lan: port 1(lan2) entered blocking state
[ 54.004845] br-lan: port 1(lan2) entered forwarding state
[ 54.010758] IPv6: ADDRCONF(NETDEV_CHANGE): br-lan: link becomes ready
BusyBox v1.36.1 (2024-03-22 22:09:42 UTC) built-in shell (ash)
_______ ________ __
| |.-----.-----.-----.| | | |.----.| |_
| - || _ | -__| || | | || _|| _|
|_______|| __|_____|__|__||________||__| |____|
|__| W I R E L E S S F R E E D O M
-----------------------------------------------------
OpenWrt 23.05.3, r23809-234f1a2efa
-----------------------------------------------------
=== WARNING! =====================================
There is no root password defined on this device!
Use the "passwd" command to set up a new password
in order to prevent unauthorized SSH logins.
--------------------------------------------------
root@OpenWrt:/#
As far as I see, no errors, now I can begin to configure WAN/Modem, LAN, Wifi and so on ...
Thank for all the help,
kind regards, thg