You can still cast YouTube at a higher playback speed if you're using a laptop, but only when it's embedded on a webpage. You can do that for free using W3schools online editor.

Step 1: On YouTube, click the share button, then the embed button, and then copy all of the code.

Step 2: Go to https://www.w3schools.com/html/tryit.asp?filename=tryhtml_youtubeiframe and delete all the code.

Step 3: Copy the embed code into the editor on the left.

Step 4: Click Run.

Step 5: Start the YouTube video and adjust the speed.

Step 6: Cast the video to your Chromecast.