Question Can I use this NVMe adapter for the M900?

You might want to stick to 2.5" SSD's instead of an NVMe adapter which is pretty hit or miss, to also add, you might want to see if there's a compatibility list for the adapter you're looking at. Chances are your platform's chipset is not supported.

To also add, we don't memorize people's specs ad builds. I might've remembered your prebuilt but you can't expect the rest of the community to do the same thing. Next time when people ask you for specs/SKU to your build, please include it.