Can't open blockdev - Error finding or mounting boot

[rewound]

Problem:
Copied using stock Raspberry PI OS 'SD Card Copier', with "New Partition UUIDs" ticked, from a running micro SD card to an empty Solid State Disk (SSD) on RPi4's USB port.
On removing SD card and rebooting just using the SSD, the screen showed:

/dev/mmcblk0 Can't open blockdev
/dev/mmcblk0p1 Can't open blockdev
/dev/mmcblk0 Can't open blockdev
/dev/mmcblk0p1 Can't open blockdev

etc etc and eventually...
Error finding or mounting boot partition :-(

Solution: Open terminal in say laptop and run as below example:
$ sudo blkid
Plug SSD into laptop USB and run $ sudo blkid again observing change as example below...

/dev/sdb1: LABEL_FATBOOT="boot" LABEL="boot" UUID="0408-696B" TYPE="vfat" PARTUUID="ea4a874e-01"
/dev/sdb2: LABEL="berryboot" UUID="91557d2c-5108-44e8-b045-def70721f05f" TYPE="ext4" PARTUUID="ea4a874e-02"

Take note of the sdb1/boot UUID it was 0408-696B
Edit cmdline.txt and add, like from example, bootdev=UUID=0408-696B and remove first redundant qmap=gb
Demount SSD and plug into RPi4 with no SD card in holder and apply power.

Background:
The original image on SD card was downloaded from
https://berryboot.alexgoldcheidt.com/search-downloads/?dl_cat=0&dl_search=Raspberry+Pi+OS+-Desktop+Basic
raspberry_pi_os_buster_desktop_basic_rpi2_rpi3_rpi4_2021.01.11_berryboot.img
Raspberry Pi OS -Desktop Basic- for Raspberry Pi 2 / 3 / 4 (2021.01.11) (1,018.3 MiB, 5,349 downloads) February 12, 2021
This is the official Debian-Optimized OS for Raspberry Pi with a (basic) desktop environment.
Code was latest as of 03 Jun 2021 using $ sudo apt update && sudo apt upgrade
Raspberry Pi OS was running on a Raspberry Pi 4

$ uname -m && cat /etc/*release
aarch64
PRETTY_NAME="Raspbian GNU/Linux 10 (buster)"
NAME="Raspbian GNU/Linux"
VERSION_ID="10"
VERSION="10 (buster)"
VERSION_CODENAME=buster
ID=raspbian
ID_LIKE=debian
HOME_URL="http://www.raspbian.org/"
SUPPORT_URL="http://www.raspbian.org/RaspbianForums"
BUG_REPORT_URL="http://www.raspbian.org/RaspbianBugs"
=====
From reportbug:
-- System Information:
Distributor ID: Raspbian
Description: Raspbian GNU/Linux 10 (buster)
Release: 10
Codename: buster
Architecture: aarch64
Kernel: Linux 5.4.73v64 (SMP w/4 CPU cores; PREEMPT)
Kernel taint flags: TAINT_CRAP
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8) (ignored: LC_ALL set to en_US.UTF-8), LANGUAGE=en_US.UTF-8 (charmap=UTF-8) (ignored: LC_ALL set to en_US.UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
=====
$ cat /proc/cpuinfo
processor : 0
BogoMIPS : 108.00
Features : fp asimd evtstrm crc32 cpuid
CPU implementer : 0x41
CPU architecture: 8
CPU variant : 0x0
CPU part : 0xd08
CPU revision : 3

processor : 1
BogoMIPS : 108.00
Features : fp asimd evtstrm crc32 cpuid
CPU implementer : 0x41
CPU architecture: 8
CPU variant : 0x0
CPU part : 0xd08
CPU revision : 3

processor : 2
BogoMIPS : 108.00
Features : fp asimd evtstrm crc32 cpuid
CPU implementer : 0x41
CPU architecture: 8
CPU variant : 0x0
CPU part : 0xd08
CPU revision : 3

processor : 3
BogoMIPS : 108.00
Features : fp asimd evtstrm crc32 cpuid
CPU implementer : 0x41
CPU architecture: 8
CPU variant : 0x0
CPU part : 0xd08
CPU revision : 3

Hardware : BCM2835
Revision : b03111
Serial : 10000000536c1b50
Model : Raspberry Pi 4 Model B Rev 1.1
=====

[rewound (rewound)]

https://github.com/maxnet/berryboot/issues/645#issuecomment-647859747
was helpful in finding the solution