Hi Diablo ,
I use debootstrap to build the rootfs image while referencing the package manifest from the xubuntu 20.04 x86 release to get it as close as possible to the official release. ( The package manifest I used is actually located in the rootfs of the image I released here ).
In regards to integrating the Jetson nano board support package /drivers, I use the apply_binaries.sh script that is included in every BSP released by nvidia with some slight modifications that allow it to apply cleanly to my rootfs. The modifications are mainly just replacing references to gdm and unity in the script with whichever display manager you plan on using, in this case lightdm. but it could be sddm or whatever the default is for the version of ubuntu you using.
For this release additional modifications needed to be made to a few of the .deb packages that are included in the BSP. I had to unpack them then change a few dependencies that conflicted with the ones included in 20.04 and repack the .deb files. most of the conflicts were related to the newer python version 20.04 ships with as the .deb’s were created for installation on 18.04.
For the modification I made to the kernel to allow kvm to work, you can take a look at this post for reference. Jetson_nano_kvm
I do plan on uploading my kernel source to github I just havnt had the time to fully learn how to use github for tracking changes to the source.
Regards,
Chris