Could we do the reverse of the instructions in the link to install and use android tv launcher on the Chromecast tv rather than the google home launcher?
These instructions show how to use the google home launcher from the Chromecast tv on a android tv device.
https://www.google.com/amp/s/9to5google.com/2020/10/02/google-tv-homescreen-android-tv/amp/
If you are confident with ADB, you can run the following two commands to disable the stock launcher on your Chromecast Google TV:
pm disable-user --user 0 com.google.android.apps.tv.launcherx
pm disable-user --user 0 com.google.android.tungsten.setupwraith
If you have another launcher installed like Wolf / ATV Launcher, the next time you press the home key, you will be prompted on which launcher you want to use. You can see my step by step guide here