Neither. In BIOS it actually specifically says M.2 slot = Empty. In Windows 10, its not showing up in Windows installer or Windows partition manager.
I have two SATA drives installed, one SSD and one standard HDD. Both of those are still visible in BIOS and Windows 10. The motherboard comes with 4 SATA ports and these two drives are plugged into 1 and 2. I will try disconnecting the SATA cables just in case now.
EDIT: Unplugging SATA cables made no difference in both BIOS and Windows installer. I also just tried changing settings from AHCI to RAID just to see if it would matter and it didn't. Also I have got a replacement coming Friday off Amazon, apparently they give you 30 days to return the original which I didn't know but I would still prefer to see if theres anything I have messed up.
EDIT 2: I saw another possible solution online from someone with the same drive who successfully got Windows 10 to see the drive using Samsung NVME drivers, I tried this too and no result. ADATA do not have any updated firmware for this device. I am currently trying another solution which worked for one guy where he installed his system in UEFI on another drive and then enabled Secure Boot and suddenly his BIOS detected it, he then installed Windows 10 to the drive and disabled secure boot and it remained working. This didn't work either, no change. I'm starting to think the drive is just dead but I will find out if thats the case tomorrow since I have a replacement coming.