Create a bootable pendrive with the latest Debian11 netinst image on it
Ensure the Nimbustor's LAN port is connected to your network - as it will need internet access during setup to fetch packages
Power down the Nimbustor
Plug a monitor into the HDMI port
Plug in the USB installer pendrive and the USB hdd/ssd you'll be installing to
Plug a USB keyboard into the 3rd USB port
Power up the unit, and keep hitting ESC on your keyboard until you get the BIOS setup screen ( you won't see any prompts as ex-factory the unit is set for silent boot)
in the BIOS settings make the following changes :
Boot
quick boot -> change to disabled
quiet boot -> change to disabled
network stack -> leave on disabled
power up in standby support -> leave on disabled
add boot options -> leave on auto
acpi selection -> leave on acpi5.0
usb boot - leave on enabled
uefi fast boot -> change to disabled
timeout -> leave on 0
automatic failover -> leave on enabled
boot order -> move usb cdrom and usb hdd to top, sdcard to bottom
sdcard/emmc -> untick
internal sata port 0 -> ticked
uefi shell -> unticked
usb hdd -> ticked
advanced / thermal
automatic thermal reporting -> leave on disabled
change critical trip point to 95 ( was 110 )
change passive trip point to 85 ( was 65 )
change active trip point to 85 ( was 95 )
DPTF -> leave on disabled ( linux doesn't really support DPTF )
advanced / cpu config
DTS -> change to enabled
leave everything else as is
advanced /security config
SGX -> change to disabled ( was 'software defined' )
advanced / system component
embedded power instrumentation -> change to enabled
leave everything else as is
advanced / south cluster / miscellaneous configuration
hide un-used LPSS devicse -> leave on enabled
PSS device - IMPJ003 setting -> change to enabled
exit and save changes ( this will cause the unit to reboot ) and proceed to the next step
Found the key to get the boot device selection: it's F5.