@Fox_exe just a little typo in the Debian install how to: you are referring to a file called rootfs-jessie.tar.xz but the filename in the repo is named jessie-rootfs.tar.gz, rather than this kernel upgrade to kernel-bin_4.15.0-rc6 and dist upgrade to stretch (Dev folder) seems worked flawlessy in ~1h but after the last reboot after dist-upgrade seems mycloud password is no longer accepted seems root account have no permission to access SSH and i’m locked out 
Also the (unbrick) bootable USB seems not booting, probably i need to erase again the HDD from a PC to avoid Debian from booting…
EDIT1:
Finally after, deataching HDD, booting recovery minios, reattaching HDD while powered on, and using the miniOS to mount debian root (was /dev/sdb3) and add my authorized_key i managed to login again.
PS. is normal that i still see old kernel with uname -r?
root@wdmc:/lib/modules# ls /lib/modules
4.15.0-rc6
root@wdmc:/lib/modules# uname -r
3.10.39
EDIT2: sorry going to use this post as my backlog
omv5 installation gone ok following Installation on Debian — openmediavault 6.x.y documentation just need to issue apt install postfix as it was searching for this package
also omv-extras OMV-Extras.org Plugin - Guides - openmediavault installed successfully with few plugins.
actually i’m locked on docker, installing from the OMV GUI started spamming “error” on the UI, looking at logs:
Apr 06 09:55:11 wdmc.fritz.box dockerd[14426]: time="2021-04-06T09:55:11.771765929+02:00" level=warning msg="Running iptables --wait -t nat -L -n failed with message: `iptables: Operation not supported.`, error: exit status 1"
Apr 06 09:55:12 wdmc.fritz.box dockerd[14426]: failed to start daemon: Error initializing network controller: error obtaining controller instance: failed to create NAT chain DOCKER: iptables failed: iptables -t nat -N DOCKER: ip
issued sudo update-alternatives --set iptables /usr/sbin/iptables-legacy as suggested around:
and actually i’m locked on
Apr 06 10:09:41 wdmc.fritz.box dockerd[16943]: time="2021-04-06T10:09:41.158961586+02:00" level=info msg="stopping event stream following graceful shutdown" error="<nil>" module=libcontainerd namespace=moby
Apr 06 10:09:41 wdmc.fritz.box dockerd[16943]: failed to start daemon: Error initializing network controller: error obtaining controller instance: failed to create NAT chain DOCKER: iptables failed: iptables --wait -t nat -N DOC
Apr 06 10:09:41 wdmc.fritz.box dockerd[16943]: Perhaps iptables or your kernel needs to be upgraded.
Apr 06 10:09:41 wdmc.fritz.box dockerd[16943]: (exit status 3)
EDIT4:
ok probably i found the culprit should be the missing iptable_nat module ( missing in 4.15.0-rc6 and also 4.15.0-plus, and this plus kernel totally killed my device so i’ll restart from the rescue mode…) probably i need to recompile the kernel but the last version is from 2016 
