Hi, Thanks for following up.
Yesterday I had a go with armbian on this device. armbian comes with a tool called: nand-sata-install (Getting Started - Armbian Documentation)
when started it let’s you choose where you want the have the root residing: usb drive is an option.
This works as advertised: the sdcard still has one partition that is used for the initial boot, but then one of the first things it does is mount the usb drive.
Exactly what I want and functional (not technical) equal to result when following this (outdated) instructions: [Tutorial - Outdated] Odroid: - Move the filesystem to a USB Drive - #3 by k-plan
So I had (!) a working armbian setup that boots from sdcard but runs from usb drive.
I say ‘had’, because when doing a kernel / firmware upgrade, the boot ‘failed’ because it was to ‘fast’ and the usb drive was not yet ready. setting a bootdelay in boot.cmd (compiled) didn’t work.
So now when booting it fails into a boot prompt where I have to type ‘exit’ and then the boot continues and all works… but in a headless setup this is a nogo :s
There where some other issues with armbian (software install via their tool not working on jammy) which made me decide that this is for my purposes not stable enough: so not an option.