initramfs after installation. "No root device specified. Boot arguments must include a root= parameter." What variable to specify?

Question

ubuntu

Good day, dear experts :)
I decided to install securely ubuntu 21.04 (5.11.0-34-generic) I did
everything according to the instructions from the article Use Secure Boot in Linux to the fullest
( habr.com/en/post/308032 )
No problems at the stage installation did not arise (tried many times).
But after installation, I boot the system, enter the password from cryptosetup and the line appears

No root device specified. Boot arguments must include a root= parameter

and then the initramfs crashes.
After I write *exit* the following pointers appear

mount: mounting /sys on /root/sys 
failed: No Such file or directory. 
mount: mounting /proc on /root/proc 
failed: No Such file or directory.

Please help, I really want to solve the problem and still install the system in this way, and not in the usual way (everything is installed automatically)
Also the output of /etc/fstab :

# <file system> <mount point>   <type>  <options>       <dump>  <pass>
/dev/mapper/ubuntu-root /               ext4    errors=remount-ro 0       1
# /boot/efi was on /dev/sda1 during installation
UUID=D263-427F  /boot/efi       vfat    umask=0077      0       1
/dev/mapper/ubuntu-home /home           ext4    defaults        0       2
/dev/mapper/ubuntu-swap none            swap    sw              0       0

What parameter to pass to the root volume and how to write it down?
I found instructions on the Internet, but they are for GRUB, but I don’t use it.
Thanks in advance for any advice.