It's been a few days and I've seen no issues.. This is more a historical post for anyone trying to take one of these old Dells and use it as a Hackintosh. Figure they'll find it in a search.

I tried doing this during the Big Sur beta release but was met with failure but at the time we didn't have a solid install process down. This time I had trouble with downloading a functional macOS install and had to rebuild the installer again. Otherwise the process seemed very similar to building a config for 10.15.

It works very well with dGPU. I was not able to get the onboard video adapter to work (Intel HD Graphics 2000.) I've ran macOS 10.15 prior with no issues. This was a fresh install on a new SSD.

Dell Optiplex 790 (tried on BIOS versions 11 and 20.)

OpenCore 0.6.3 (following this guide: https://dortania.github.io/OpenCore-Install-Guide/config.plist/sandy-bridge.html) It might look complicated but if you go LINE BY LINE you'll find success!

*** Important Note: The Dell BIOS does not read the EFI partition generated by macOS's disk utility. It *WILL* crash BIOS and you will not be able to add it to your EFI boot list.I recommend using Windows diskpart to reformat the partition to fat32 and then drop your EFI on it. You'll need to do this twice: Once on the install medium, second on the storage you installed macOS.

^{Example on Windows: diskpart, list disk, sel disk #, sel par 1, format fs=fat32 quick - I don't recommend using macOS's diskutil to format; it caused SSD corruption when I modified the EFI partition. You however CAN use it later to mount the EFI to copy/modify your config (sudo diskutil list, sudo diskutil mount /dev/disk#s# \}probably disk0s1]))

Recommend you update to BIOS version 20 if you're using USB to install; lesser versions seem to fail with USB boot of OpenCore 0.6.3. If you don't want to update, use an SSD as your installer attached to SATA.

Sandybridge Intel Core i5 @ 3.1GHz
Nvidia GeForce GTX 660 Ti 2GB (supported, glad I found a use for it!)
SMBIOS iMac 15,1
Audio: layout-id 0F000000

SSDT-EC, SSDT-HPET required
HfsPlusLegacy.efi required
IntelMausi.kext required for onboard networking; if you don't add this you'll have issues with iCloud.
Do NOT select TRUE for CustomSMBIOSGuid (guide says to do this if Dell, don't.)

I'm also using Chris1111's Wireless USB Adapter drivers for my RT wifi dongle with no issues.

Good luck. If you have any issues you can reach out.