I didn't do anything. everything is default unraid install.
However, i managed to solve the issue with the help of the post below. Apparently i need to make an empty file,
- Run this in unraid terminal to create the empty file:
touch /boot/config/modprobe.d/i915.conf
- make sure all Windows VM display is set to VNC and not to the integrated GPU.
After that, restart and the /dev/dri is there.
Although i still don't understand how in these days of modern operating system we need a single empty file to make things work.
Thanks all for the support.