I would like to help clarify some confusion around the different interfaces used by HP and in the industry with M.2 drives
First of all, M.2 can be used with either a ahci/sata interface connetion or a pci-e connection. A pci-e slot designed for an SSD (unlike, say, a wifi card) takes up x4 speeds tos upport the high transfer rates of SSD technology
Now, HP calls a PCI-e SSD connection (Turbo Drive), and we have both PCI-e M.2 as well as true PCI-e cards available for different chassis choices.
The Desktop Mini chassis supports the following as boot media:
600 or 800 G1: M.2 PCI-e with ahci/sata connection (HP Turbo Drive G1)
600 or 800 G2: M.2 PCI-e with ahci/sata OR NVME connection (HP Turbo Drive G1 or G2)
So, a 3rd party M.2 PCI-e SSD with an ahci/sata controller will work in both G1 and G2 desktop minis, while a M.2 PCI-e SSD with a NVME controller will only work on G2 systems
Hope this help clear out confusion around what works and what does not work