Basically it would be recommended to move the whole system or at least the rootFS to a USB pen stick or SSD.
How to move the whole system we describe on our blog. If you are not planning to shrink the file system size, some parts maybe obsolete. https://dietpi.com/blog/?p=1236
another user guide on our forum https://dietpi.com/forum/t/raspberrypi4-rpi4-upgrading-from-existing-sd-card-setup-to-boot-from-ssd/4555/1