Erro: comando falha: adb shell am start -n
First of all make sure you have set the permanent java jdk path correctly https://www.javatpoint.com/how-to-set-path-in-java
Right click on the android folder in your react native project and open with command promt and type "gradlew clean"
3.Navigate to your root project folder,right click and open with cmd and type "react-native run-android"
This worked for me. Link https://www.youtube.com/watch?v=voYoKf0WUyk
Santino