@ssumpf sorry, I’m struggling to assemble an option for a couple of partitions on the disk (I don’t want to use the whole disk, just 1st and 3rd partitions with biod_boot and linux root filesystems) 
Could you please provide an example how to correctly do this in the option file? 
Oh, btw, EFI supported without any issues at the moment?
Yes, EFI is supported (Windows/Linux guests).
You should be able to pass two partitions to VBox7. I would follow Johannes approach https://genodians.org/jschlatow/2021-04-23-start-existing-linux-from-sculpt:
VBoxManage internalcommands createrawvmdk -filename disk.vmdk \
-rawdisk /dev/<sdaX or nvmeX> -partitions 1,3 -relative
block node the runtime, e.g.,+ block sda1 | label: 1 | io_buffer: 8M
+ block sda3 | label: 3 | io_buffer: 8M
+ connect node+ block | label_last: 1 | + child nvme-1.part | label: 1
+ block | label_last: 3 | + child nvme-1.part | label: 3
This is just a rough sketch and I will leave figuring out the details up to you.
Thank you a lot!
Will try that today! 
@ssumpf it works great now! Thank you!
I even dared to connect the gpu to intel_gpu, play and record to the mixer, and rom (mesa) to mesa_gpu-intel (had to tweak that one to start the component on my i7-10700 first)!
So VirtualBox starts and loads my system, though I still have some challenges ahead.
Because my Linux system is a bit unusual: Artix with OpenRC, XLibre and i3 as a window manager.
Looks like it shows only the background picture and nothing else despite of actually running the apps I start with dmenu. 
Though with mesa_gpu-cpu it was extremely slow but at least draw a Telegram window once 
But I guess this thing is on the VBox itself, rather than on the Genode 
Ok, turned out the issue was in a picom running using glx.
Disabled it and now everything is fine! 