I’m sure there would be a way to do this with Debian, but I have to confess I don’t know it. I have successfully done this in the past with Clover Bootloader. You have to enable an NVMe driver, but once that’s done you should see an option to boot from your NVMe device. After you’ve booted from it once, Clover should remember and boot from that device automatically going forward. I used this method for years in a home theatre PC with an old motherboard and an NVMe drive on a PCIe adapter.