Ubuntu won't boot: Kernel Panic - Not Syncing Attemptted to kill init

I have Ubuntu 20.04 and windows installed in a dual boot. Suddenly my ubuntu won't boot and shows this error

end Kernel Panic - not syncing: Attempted to kill init

I've tried several solutions:

1. at grub menu I entered advanced settings and I got 4 options to boot intoadvanced settings

   I tried all of them and they all produce the same error

2. using boot repair also didn't work

3. using a ubuntu live-usb:

   • I checked sda6/sbin/init and it does exist.

   • I tried sudo fsck /dev/sda6 and the output is:/dev/sda6: Clean

   • Disabling selinux :I mounted the partition using sudo mount /dev/sda6 /mntbut I can't find the file /etc/selinux/config as only semanage.config exists in selinux folder.

   • reinstalling init:I mounted the partition using:

     sudo mount /dev/sda6 /mnt

     but I can't access my root's env using sudo chroot /mntas I get the error:

     chroot: failed to run command ‘/bin/bash’: No such file or directory

Where do I go from here to solve the problem ?

sources:1- https://askubuntu.com/questions/92946/cannot-boot-because-kernel-panic-not-syncing-attempted-to-kill-init

2- How to solve "Kernel panic - not syncing - Attempted to kill init" -- without erasing any user data

3- https://itectec.com/ubuntu/ubuntu-debugging-kernel-panic-not-syncing-attempted-to-kill-init/