I tried to never connect my Smart TV to anything, but I realized one day (when someone's stuff was playing on it without me accepting any request...) it connected an open network in my residence.
The only trick that worked to prevent it from connecting was putting the wrong password, and let it loop forever, trying to connect. Ugly.
Lots of consumer routers these days let you set parental controls. Disable access entirely, or put time limits on it, then remove all the allowed times.