Be aware of the following points that are not mentioned in that tutorial:
- you need 2 GPUs in your system. 1 for the VM and 1 for truenas. Truenas wont allow you to passthrough your only GPU
- the GPU or whatever device you want to passthrough, needs to be in its own IOMMU group.
- you also need to passthrough the audio device belonging to your GPU.
This tutorial uses a monitor, that is locally attached to the Truenas machine. Is this also what you are planning ?
If you want remote access, i suggest Parsec (its seems to be available for Mac OS).