“Hide from Screencast” is a frequently used action such as “Keep above windows”, so having it as a decoration button would provide quicker access than having to find it under “More Actions” each time
I think, iirc, it already is a button that you can add to the title bar or your windows. Not at my computer right now, but you should be able to find it in System Settings in the same place you add/remove buttons from the window title bar.