Answered Template variable that hides post author when checked

Use output Modifiers.

https://docs.modx.com/revolution/2.x/making-sites-with-modx/customizing-content/input-and-output-filters-(output-modifiers)

create the TV, and the value when is checked.

then use something lie this: [[*tvNameHere:is=`ValueTVHere`:then=`[[*publishedby:userinfo=`username`]]`]]

The code will looks for the value of the tv, if the value is for example Yes, then it will display the published by, if is not Yes then it will hide it.