Call GetDeviceCaps failed when remote desktop is minimized

I try to run a demo of d3d9 in a windows 10 virtual machine only with a NVIDIA RTX 3090 card. This windows vm is connected via windows remote desktop. Here is my demo:

#include <Windows.h>
#include <d3d9.h>
#include <stdio.h>

int main() {
    // sleep 5 seconds and manually minimize the remote desktop window immediately after the sleep operation
    Sleep(5000);

    IDirect3D9* pD3d9 = nullptr;
    
    pD3d9 = Direct3DCreate9(D3D9b_SDK_VERSION);
    
    UINT adapters = pD3d9->GetAdapterCount();

    for (UINT i = 0; i < adapters; i++) {
        D3DCAPS9 caps = {};
        HRESULT res = pD3d9->GetDeviceCaps(i, D3DDEVTYPE_HAL, &caps);
        if (FAILED(res)) {
            printf("Call GetDeviceCaps Failed:%x\n", res);
            break;
        }
    }

    pD3d9->Release();
    return 0;
}

GetDeviceCaps return S_OK when the remote desktop is a window or fullscreen mode. But, when running this demo in a minimized remote desktop, GetDeviceCaps return a error code: D3DERR_NOTAVAILABLE.

Does anyone know what is causing this call to fail?

Thanks!

When 'minimized' legacy Direct3D 9 does NOT have access to the GPU. This is part of the emulation of legacy behavior. Direct3D9Ex or later are WDDM aware APIs, and support accessing the GPU when 'screen locked' or 'minimized' in cases where legacy Direct3D does not.