Suggestion: DX12 Upload Heaps: use a CPU thread as a copy engine:

[Logic-Elliven]

"...With the VRAM being managed by Windows, D3D now exposes the heap memory access directly to the CPU! This allows both the CPU and GPU to directly access the memory simultaneously..."
https://devblogs.microsoft.com/directx/preview-agility-sdk-1-710-0/

"...Copy engines can execute copy commands in a COPY queue concurrently with other GPU work, and multiple COPY queues can be used concurrently. One problem with using async COPY queues though is that you must take care of synchronizing the queues with DX12 Fences, which may be complicated to implement and may have significant overhead.

The latest release of the Microsoft provides an alternative solution for DX12 applications to effectively use a CPU thread as a copy engine. This can be achieved by creating a DX12 GPU upload heap (D3D12_HEAP_TYPE_GPU_UPLOAD) if available. CPU writes to this GPU upload heap are then forwarded directly to VRAM, over the PCIe bus..."
https://developer.nvidia.com/blog/optimizing-dx12-resource-uploads-to-the-gpu-using-gpu-upload-heaps/