Appreciate the help, but unfortunately, VRAM has nothing to do with this issue.
On an i9-12900k, 32gb DDR5 RAM, 3080 Ti, Windows 11, latest Nvidia drivers – I moved everything from ULTRA to HIGH on DX12.
Same result, still have GPU Mem to spare.
Just based off these forums, it seems anyone with a 3090 has no issues w/ DX12. Everyone else does. A 3080 Ti is completely capable of DX12 and should have zero issues.