You copied from
/dev/nvme0n1 to /dev/sdc and now there are problems with /dev/nvme0n1? Please confirm. Or is the problematic nvme0n1 the disk that used to be sdc? The question is not clear. Did you replace the old device with the new? Or did you try to boot from the old one (possibly with the new one connected)? Or did you try to boot from the new one (still in the external case)? Please [edit] and clarify.