Now, many here will already know this, and/or maybe even doing it. Still, finding this info through any search process appears, to this one, to be non-existent. As I run Debian (testing), am posting to the Debian forum, but every Linux distribution should work the same.
It is well documented that to boot an Operating System from a PCIe NVMe drive it must be supported in the BIOS. Note; the key word for this exercise is boot. Nothing about run

Yes, even without motherboard support, Linux can be used and run on a PCIe NVMe drive. Attach drive to adapter card, put adapter in PCIe slot, then boot the install process (CD/USB stick, etc.). Nothing changes during this installation process to the PCIe NVMe drive except:
**** The /boot partition and the boot sector must both be installed to the boot drive (/dev/sda for most?) ****
Hey presto, bingo and Bob's you're aunty. Install finishes, reboot and you are running from the PCIe NVMe drive/
Romane