It should have support for casting your screen to a Smart TV but after Android 5.0 Google disabled Miracast at the system level in favour of their proprietary Chromecast. Miracast can be enabled but only through rooting or via the manufacturer enabling it.
Also I don't know why but the 'Cast' option can be found only if we tap search icon in the 'Setting' Menu by typing 'cast'. And there is an option for Wifi Direct in the Wifi settings if you have a device that supports casting through that.
The cast option should be in quick settings if you choose the pencil to edit them.
That's odd, it's there on my Nokia 8 but then I have Android 8.1 instead. Having said that the Cast quick setting has been there since before Android 5.0
I was just using my phone as a comparison, that's all. I think it must be a bug.