well i think for the deck it should be kept off as i dont see any use for iommu on the deck as it does not even support eGPUs, if it did support eGPUs then i would see a point in keeping it enabled. i just remembered my iommu kargs got removed once when i ran the deck image (before i rolled my own just to streamline testing)
I was already using Silverblue as my main desktop, then saw what Jorge was doing with OCI images and had a brief "wow that's cool, you could make a better SteamOS with this"