Welcome to Android Central! It can be confusing when you have both the Android app and the PWA (progressive web app) installed. If you don't want to use the Android app on your Chromebook, then locate the icon in the launcher right-click it, and then Uninstall it. Then in the browser, go to the YouTube site, and look for the Install App option at the right of the URL bar. This will install the PWA. Now when you click the YouTube icon in the launcher, it will open the PWA rather than the Android app.