I know that cold brew is a thing of black teas, its just that it takes a while to do black cold brews, compared to gyokuro which you can brew it room temp under a min or so if you're using higher ratio of tea to water compared to western brewing.

But yes like I mentioned you can do green tea near boiling its just it depends heavily on where its from, how its grown, how its treated and how fresh it is. The less fresh green tea is, the colder the water you should be using.