https://preview.redd.it/hx19bwhz5l3d1.png?width=1389&format=png&auto=webp&s=c6732806c85cc087551d24e6cfbe8d40c5263a70

https://preview.redd.it/eiikssci6l3d1.png?width=770&format=png&auto=webp&s=78f93c45a0be2dd3fe3aa3dff26cd5c2d24a37f5

Hardware

• CPU: Sandy Bridge Core i5
• GPU: NVIDIA GeForce GT 730 (Kepler)
• RAM: SK Hynix 8 x 3 = 24 GB
• Motherboard Make and Model: Intel Q67 Express
• Audio: layout 1 (I forgot the exact codec)
• Ethernet Card: Intel
• BIOS revision: A24 (latest)

Which of the guides on the sidebar you used: dortania

Important

The default method of USB creation will NOT work. You have to first restore the BaseSystem.dmg on your USB volume, using the TransMac software (free trial). Then use the Paragon Partition Manager to create and format a 200+ MB FAT32 partition before the BaseSystem partition. DO NOT name the partition as "EFI". You can name it anything other than "EFI" like "MACEFI", for example. There is a bug on the system firmware where it freezes if the EFI volume is also named "EFI". Then put your OpenCore EFI folder on the "MACEFI" volume and boot into it. Do the same after installing macOS. You will also need to manually point to BOOTx64.efi in the BIOS menu (the "Add boot option" menu) for booting. (I have not tested using LauncherOption).

BIOS settings:

• UEFI mode
• Serial port: COM1
• Enable "Intel Execute Disable"
• AHCI mode

Notes:

• Some USB ports weren't working so I did the USBMap after installation.
• I cannot get my Pixel phone to work as a webcam, which I was able to do on Windows.
• I have tried the same config on both Optiplex 990 and 790, and it works; YMMV.

Edit: Formatting errors.