I recently needed to clone over a smaller NVMe to a 2TB SK Hynix Platinum P41 NVMe, however I ran into the issue where it was not bootable.

The fix

Using Mactrium Reflext the cloned NVMe was not bootable, the solution to this was to use the SK Hynix SSD system migration utility tool.

This then actually fully cloned over my smaller OS NVMe to my SK Hynix Platinum P41 NVMe and it was bootable.

So whilst Mactrium Reflext is highly regarded and suggested, it never worked for me in this situation. Instead using the actual SK Hynix branded migration tool worked and this is also seemingly made by Macrium.