Q. How can I increase the VRAM assigned to a VM with Windows Server 2016 Hyper-V?
A. When using RemoteFX the amount of VRAM can be specified either through the graphical management tools or via the Set-VMRemoteFx3dVideoAdapter cmdlet and the -VRAMSizeBytes parameter. If not using RemoteFX then a resolution can be configured along with a resolution type that will set the amount of VRAM based on that target resolution.
Set-VMVideo -VMName "<VM name>" -HorizontalResolution 1920 -VerticalResolution 1200 -ResolutionType Maximum