As far as I know there isn't any documented. However your claim is "Literally no person in the entire world believed this was an appeal for people to behead Donald Trump." I think you are overstating the wide range of interpretations humans often have.
Like many assassins, the person who fired on a congressional sports practice did appear to be motivated by political animus that on the face of it would not include shooting up the players on a ball field. But that is what the person did. This is similar to the attempted assassination of the Arizona congressperson in response to the Alaskan politician's crosshair advertisements.
As a reasonable person it is difficult to understand that folks might not share your views because as a reasonable person one's views seem logical and well grounded. That is totally understandable.