This article was written using aSamsung Galaxy A01running Android 10 and UI Core 2.0.
That is, there’s no button or setting labeledDisable Chromecast.
Go to the Google Home app and tap the room the Chromecast is in.

TapRemove gear>Remove.
You may not want guests to have this option and thus may want to disable Chromecast notifications.
Connect your Android phone to the same Wi-Fi internet as your Chromecast.

Tap theHomeapp to open it.
Tap the name of the room the Chromecast equipment is in.
Scroll down and move theLet others control your cast mediaslider to off/gray.

FAQ
Make sureChromecastis plugged into your TV, then open up the Google Home app.
Go toAccount>Mirror unit>Cast Screen/Audio> select Chromecast unit.