[Const-me]

> Are there APIs which can sidestep the "load to CPU RAM" part?

On windows that API is Desktop Duplication. The API delivers D3D11 textures, usually in BGRA8_UNORM format. When HDR is enabled you would need slightly different API method which can deliver HDR frames in RGBA16_FLOAT pixel format.

[mmozeiko]

There's also Windows.Graphics.Capture. It allows to get texture not only for whole desktop, but just individual windows.