Booting from mtd/nvme should just work.
Most common problems:
- dirty mtd/emmc. vendor/unmatching boot loader can cause issues.
- mixup between m.2 sata and actual nvme. Correct overlay/dt must be used
- wrong rootfs uuid in armbianEnv.txt after running armbian-install (after done, do not reboot but mount freshly written nvme to a random folder and check if the uuid is correct)