I was using the android-ndk download via Android studio plugin. Open Android Studio Go to Settings > Appearance and Behavior > System Settings > Android SDK Click SDK Tools tab Check Show Package Details. The studio will ask you the path of the Android SDK.
If not, then follow this post to install it manually. But when I did I tried to update it but it wouldn't work so I had to launch: C:\Users\username\AppData\Local\Android\sdk\tools\android.bat to install other packages. Downloaded the 64bit version and browsed the net to find tips on configuring gradle. Without ndk-bundle folder in /opt/android-sdk, the Flutter tell that ndk isnt. Well if you have installed the Android Studio for the first time, then you will be guided towards installing the Android SDK. My android studio said it wanted to update. The NDK is a software release that is available as a freed download from within the Android Studio environment.