So I just did
sedutil-cli --setLockingRange 0 rw "..." /dev/nvme0n1 and was still greeted with a locked drive. As evidenced by:
mount: /mnt/nvme0: wrong fs type, bad option, bad superblock on /dev/nvme0n1, missing codepage or helper program, or other error.
The solution was found in a shell script within
rear, the “Linux bare metal disaster recovery and system migration solution”.
The following commands then did the trick and the drive was mountable again:
sedutil-cli --setMBRDone on "..." /dev/nvme0n1
sedutil-cli --setMBREnable off "..." /dev/nvme0n1
Looks like the drive was still expecting some pre-boot stuff to happen. The latter command disables this.