Grub:

GRUB_DEFAULT=0
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="Proxmox Virtual Environment"
GRUB_CMDLINE_LINUX_DEFAULT="quiet amd_iommu=on iommu=on video=vesafb:off,efifb:off"
GRUB_CMDLINE_LINUX=""

VM:

bios: ovmf
bootdisk: scsi0
cores: 8
efidisk0: local-lvm:vm-300-disk-1,size=128K
ide0: local:iso/virtio-win-0.1.172.iso,media=cdrom,size=363104K
ide2: local:iso/Windows10-1903.iso,media=cdrom
memory: 16384
name: gameserver
net0: virtio=B6:94:31:C7:39:8F,bridge=vmbr0,firewall=1
numa: 0
ostype: win10
scsi0: local-lvm:vm-300-disk-0,size=60G
scsihw: virtio-scsi-pci
smbios1: uuid=d43980a6-7f9e-4587-be17-020a1cbf8925
sockets: 1
vmgenid: 566d246a-b6a9-45d3-a164-751b27697394

Modprobe.d contents:

cat /etc/modprobe.d/blacklist.conf
blacklist radeon
blacklist nouveau
blacklist nvidia

cat /etc/modprobe.d/kvm.conf
options kvm ignore_msrs=1

cat /etc/modprobe.d/vfio.conf
options vfio-pci ids=1002:67df,1002:aaf0 disable_vga=1