Thank you everyone for all the amazing advice on this thread. It saved me from yanking all my hair out during this process.
I naively purchased a EVO 970 NVME M.2 and a
Mailiya M.2 PCIe to PCIe 3.0 x4 Adapter hoping to use this as my main boot drive with Mojave.
The NVME drive shows up as an External Disk. So I ordered a
Angelbird Wings PX1 PCIe x4 M.2 Adapter
Again the same problem, the disk shows up as an External Disk. I've moved it around from Slot 2 to 4 with no luck.
I have Erased it, formatted as Mac Journaled Case Sensitive and MS DOS etc - no luck. I don't see the APFS option when trying to format it.
I'd like to realistically use this as PCI/NVME as a boot drive with a fresh install of Mohave (I was reading that Mojave has to be installed as an upgrade)
View attachment 805340
MacPro 4,1 -> 5,1
2 x 2.4Ghz 6 Core Xeon
32GB RAM
MSI Radeon 560
macOS: 10.14.1
BootROM: 140.0.0.0