Am unfortunately not able to go through all those videos, but will watch a couple. Thanks!
And viruses don’t defy gravity - they have to adhere to the physical laws of nature just like any other organism. If it got into the vent, it got there by an explainable reason.
I know...I was dramatizing the point a bit...Intuitively we thing stuff goes down, not up... :-)
At a sufficiently small particle scale, Brownian movement will disperse a material throughout an enclosed space, without the aid of convection.
The air blows upward out of the outlets. No big mystery there.