You cloned "sdc1" which is a single partition however it sounds like you are attempting to clone an operating system which means you also need the boot-programs.
The location of that information will vary depending on how you have things setup. For example if you are using an MBR partition table then it's stored in the drive MBR, if you are using GPT with BIOS then it's stored in the drive's protected MBR, if you are using GPT with UEFI then it's stored on the ESP, and if you are chain-loading then you could have boot-data on a partition MBR, and the drive MBR.
DD can be used to clone MBR sectors, or an ESP. Alternatively you could just clone the entire drive to save yourself the trouble of making multiple images. I personally recommend avoiding the cloning of MBRs as I've only tried it once, and without success. ESPs or entire drives have always worked fine for me no problem.
My examples below use the creation of an image, and then restoring from it since that's the approach that you are using, but for the record if you can connect both usb sticks to the computer at once you can directly clone from 1 to the other without making an image.
Steps:
Backup Drive MBR & Partition Table:
In terminal type "sudo -i".
In terminal type "dd if=/dev/sda of=/media/location/backup.img bs=512 count=1".
Restore Drive MBR:
In terminal type "sudo -i".
In terminal type "dd if=/media/location/backup.img of=/dev/sda bs=446 count=1".
Backup Partition MBR & Partition Table:
In terminal type "sudo -i".
In terminal type "dd if=/dev/sda1 of=/media/location/backup.img bs=512 count=1".
Restore Partition MBR:
In terminal type "sudo -i".
In terminal type "dd if=/media/location/backup.img of=/dev/sda1 bs=446 count=1".
Backup An ESP:
In terminal type "sudo -i".
In terminal type "dd if=/dev/sda1 of=/media/location/backup.img".
[This process is exactly the same as cloning any other partition.]
Restore An ESP:
In terminal type "sudo -i".
In terminal type "dd if=/media/location/backup.img of=/dev/sda1".
Backup A Partition:
In terminal type "sudo -i".
In terminal type "dd if=/dev/sda1 of=/media/location/backup.img".
Restore A Partition:
In terminal type "sudo -i".
In terminal type "dd if=/media/location/backup.img of=/dev/sda1".
[RECOMMENDED ACTION] Backup A Drive:
In terminal type "sudo -i".
In terminal type "dd if=/dev/sda of=/media/location/backup.img".
[RECOMMENDED ACTION] Restore A Drive:
In terminal type "sudo -i".
In terminal type "dd if=/media/location/backup.img of=/dev/sda".
Notes:
It's recommended that DD be run as root, not sudo as otherwise interruptions could potentially occur. On Ubuntu this is difficult given you cannot login as root.
When restoring MBRs you can use 512 or 446. 446 will just restore the MBR (where your boot-strap code & boot-loader are written). 512 will restore the MBR and the partition table.
You don't have to make an image; you can clone directly from source to destination.
Sources:
Additional Resources:
Best Answer
Full Install USB vs Persistent install
A Full install USB and a Persistent install USB both save data and installed programs after reboot.
Comparison between Persistent and Full install USB
Advantages of a persistent install:
You can use the persistent pendrive to install Ubuntu to another computer.
A persistent install takes up less space on the pendrive.
You can reset the pendrive by overwriting the old casper-rw file with a new one.
The install to pendrive takes less time.
Advantages of a Full install:
You can update and upgrade.
If you have problems or wish to modify, the solution is the same as with an internal install, (You can ask for help in these forums).
No ugly startup / install screen.
Better security, you can use full encryption
You can use proprietary drivers.
Hibernation works.
A persistent install is limited to a 4GB casper-rw and a 4GB home-rw persistence file, to get more persistence requires persistence partitions. Once casper-rw is full, the drive will not boot. YUMI and Universal can use persistent files greater than 4GB when installed on a NTFS partition and in BIOS mode. Ventoy can also use persistent files larger than 4GB.
Faster boot.
You can run VBox and use virtual machines.
Note that once booted, both methods run at about the same speed.
Full Install Method
One method for creating Full install USB: How to Create a Full Install of Ubuntu 20.04 to USB Device Step by Step