If you open your encrypted container as for example Encrypted using the crypttab or luksopen command then:
You would need:
linux /boot/vmlinuz-5.15.0-58-generic root=/dev/mapper/Encrypted ro quiet splash $vt_handoff
And also use the same /dev/mapper/Encrypted in your /etc/fstab …
Otherwise you are NOT using the contents inside the encrypted container as root file system…
This has nothing todo with which distro you use, it is how you mount the root filesystem that is inside an encrypted container…