кстати, они этот способ деприкейтят и просят в build.gradle указывать:
The value for ndk.dir should no longer be set in your app's
local.properties file, and support for this ndk.dir setting will be removed in a future version. The Android Gradle Plugin sets the NDK version by default, but if you need a specific version of the NDK, you can set android.ndkVersion in build.gradle