I have a Dell Optiplex 5090 MT desktop  1. The SSD I have is an Apacer AS2280P4 512GB SSD. It is M.2 PCIe Gen 3x4. 2. Yet when I look in the BIOS, I can see the Apacer SSD listed in storage drives. 3. I was trying to install Windows 10 Pro but when it comes to the part where I select the drive to install Windows 10 on, the drive does not appear.  4. I tested with a SP 128GB M.2 2280 SATA III SSD. The same problem is encountered.   1. Where do yall find these strange off-brand SSDs ? 2. Good. Step one complete. 3. SSD must be completely blank. Like DiskPart-Cleaned blank. Also, it should be the only drive currently connected. Also set BIOS as below. 4. Be sure BIOS is set to UEFI/AHCI/SecureBoot. Also, see #3 above.  
I have a Dell Optiplex 5090 MT desktop with a default storage of 1TB HDD. I want to install a 512GB M.2 SSD. The SSD I have is an Apacer AS2280P4 512GB SSD. It is M.2 PCIe Gen 3x4. I was trying to install Windows 10 Pro but when it comes to the part where I select the drive to install Windows 10 on, the drive does not appear. This made me think the computer doesn't support it. Yet when I look in the BIOS, I can see the Apacer SSD listed in storage drives. I tested with a SP 128GB M.2 2280 SATA III SSD. The same problem is encountered. I checked if it has anything to do with security settings. No luck.
Adding a M.2 SSD to Optiplex 5090 MT