You should look around to find videos or more comprehensive tutorials for this. This is a useful skill to have if you are Linux user. So many breakages can be solved by using this.

For chrooting you first have to boot a live ISO (you did this for installing Ubuntu). You can use an Ubuntu live ISO but it’s not necessary. It should work with most distros.

Then open the terminal. (Or not. You can do this from the TTY as well.)

After that you mount your file system to a mount point (typically /mnt but can be whatever). You can do this by running the following commands. PLEASE DON’T BLINDLY COPY PASTE. Replace /dev/sda1 with whichever devices is mounted to / for your system:

# mount /dev/sda1 /mnt
# mount -t proc proc /mnt/proc
# mount -t sysfs sys /mnt/sys
# mount -o bind /dev /mnt/dev
# mount -t devpts pts /mnt/dev/pts
# chroot /mnt

After this you should be able to use apt to install whatever you had uninstalled.

Here I am making some assumptions:

• you are not using disk encryption
• your / file system is supported by the kernel natively (that you are not using something like zfs)

So if any of these is the case then you will have to adapt accordingly.

When done you can exit the chroot and umount. Then try rebooting to see if the problem is fixed:

# exit
# for point in /mnt{/dev/pts,/dev,/sys,/proc,}; do
>   umount $point
> done
# reboot

I think your advice seems to mostly be sound. I think the execution of the advice was the problem :)