aperture

I have an Intel CPU with embedded iGPU (i5 1335u) on my proxmox host and 16Gb of ddr5. In host bios, i can chose 128-256-512-1024 memory aperture for the iGPU. This amount of memory is later no more available in proxmox host (reserved) I wonder, if the GPU is shared between several VMs ( vGPU )...