Today I have installed Kubuntu (without modifying EFI, with
ubiquity -b
I choose btrfs as filesystem, and the root is with subvolumes (@ and @home).
I had to add symlinks to the root folder so that update-grub, in KDE-Neon (on the same PC) could recognize Kubuntu.
The new Kubuntu partition is displayed without errors in KLDE-Neon.

But if I try to boot Kubuntu, I get a kernel panic error message:
mounting /dev on /root/run failed: no such file or directory
and similar others.

What should I do?
Thank you!