My new Chromcast is not in the Stadia launch menu. Additionally, the ambient menu option for Stadia codes is not displaying. I have factory rest the device and the firmware is currently 1.52 or later. Other smart TV's are available to launch from the Stadia menu and an old Chromcast is available but the new one is not visible.
Hey there!
If you have a Chromecast with Google TV, you just need to install Stadia through Google Play.
Additionally, "normal" Chromecasts (not Ultra) do not support Stadia at this time.