Yarn ios or react-native run-ios not running react native app

I have created a react-native app using create-react-native-app package. Now running the app using yarn android to run in android emulator works fine. It auto starts the metro builder. But, in case of iOS, using yarn ios does not auto start the metro builder so I have to run it manually and then run yarn ios command to run the app in iOS simulator.

Why is this happening?

Also, in case of android, I have to change the gradle version as well otherwise it gives me error:

Error:Could not initialize class org.codehaus.groovy.runtime.InvokerHelper

But, checking the version using gradle --version shows version 6.5. I need to change gradle-5.6.3-all.zip to gradle-6.3-all.zip or above in file gradle-wrapper.properties. Is there any permanent way to solve this?