The previous site already shows this in practice, but here’s a more technical explanation for you

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/virtualization_deployment_and_administration_guide/sect-iommu-deep-dive

Here’s some more real life examples: https://forum.level1techs.com/t/vfio-passthrough-in-2023-call-to-arms/199671/18

https://old.reddit.com/r/VFIO/comments/16czih3/how_to_find_a_motherboard_with_good_iommu_groups/

Passed that you can take your skepticism somewhere else, I don’t really care that you don’t believe me, it doesn’t change the reality of how IOMMU groups work.

Grouping has become overall better since X570, but still not a given.