I just found it after looking thru the FAQ's. In the video box at the bottom right of the screen, find the little window and hover your mouse to find the one that says "Chromecast". Then it searches for your TV. When it pops up, click on it and you're all set.

I have noticed the same thing. The videos do not cast to my Samsung TV from my laptop. I really wish they would. Now I have to use my small laptop and have no way to control it remotely 😒