I asked because this
"This is an application which allows the SD card inserted into the Pi to be copied to one in a connected USB reader."
is at the top of the readme. I have no idea if piclone runs under LibreElec and if not how to use it, nor why it should be any more effective than those I've tried so far.
You now seem to be recommending a clean install and restore backup not cloning which is what I want to do. I know I was able to clone a 32GB to a 64GB microsd card and then resize the 64GB card's storage partition but going from 128GB to 128GB seems impossible.
I haven't tried your idea of "preparing" the card (which I'm assuming means install LibreElec and then overwrite stuff) because my Linux PC doesn't want to recognise one card in its microsd slot and another one on a usb adapter at the same time.
Why this is proving such a challenge I do not know but would like to.