Install the deb package with dpkg: dpkg -i /tmp/i915-sriov-dkms_2025.05.18_amd64.deb
Once finished, the kernel commandline needs to be adjusted: nano /etc/default/grub and change GRUB_CMDLINE_LINUX_DEFAULT to intel_iommu=on i915.enable_guc=3 i915.max_vfs=7 module_blacklist=xe, or add to it if you have other arguments there already.
Update grub and initramfs by executing update-grub and update-initramfs -u
Optionally pin the kernel version and update the boot config via proxmox-boot-tool.
In order to enable the VFs, a sysfs attribute must be set. Install sysfsutils, then do echo "devices/pci0000:00/0000:00:02.0/sriov_numvfs = 7" > /etc/sysfs.conf, assuming your iGPU is on 00:02 bus. If not, use lspci | grep VGA to find the PCIe bus your iGPU is on.
Reboot the system.
When the system is back up again, you should see the number of VFs under 02:00.1 - 02:00.7. Again, assuming your iGPU is on 00:02 bus.
You can passthrough the VFs to LXCs or VMs. However, never pass the PF (02:00.0) to VM which would crash all other VFs.