It isn't. Nvidia & AMD just charge a massive premium for the privilege. Nvidia calls it vGPU https://docs.nvidia.com/grid/13.0/grid-vgpu-user-guide/index... and AMD calls it MXGPU https://www.amd.com/en/graphics/workstation-virtual-graphics
Both have been around for a while now, and both refuse to bring it to their consumer cards.