Android Studio NDK being incompatible though having been set properly

I am trying to integrate OpenCv with android studio and in the process NDK issues are being faced by me . The NDK always remains unselected in the Project Structure.The header files always remain unavailable because the path get unmentioned . I am trying to resolve this issue since days but not able to find the solution of the above if someone would help. The NDK does not connect , though having been tried many ways to integrate NDK. I had used all possible ways of integrating the NDK and have taken possible measure to replicate my needs but nothing works. I have seen how others tried to resolve the issue but none of those worked for me.

Here below is my code CMakeLists.txt file

cmake_minimum_required(VERSION 3.4.1)

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")

include_directories(${OpenCV_DIR}/jni/include)

add_library( lib_opencv SHARED IMPORTED )

set_target_properties(lib_opencv PROPERTIES IMPORTED_LOCATION ${OpenCV_DIR}/libs/${ANDROID_ABI}/libopencv_java4.so)

add_library( # Sets the name of the library.
             native-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             native-lib.cpp )

find_library( # Sets the name of the path variable.
              log-lib

              # Specifies the name of the NDK library that
              # you want CMake to locate.
              log )

target_link_libraries( # Specifies the target library.
                       native-lib

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib}

                       lib_opencv)

native-lib.cpp

#include <jni.h>

Here above the jni.h file is linted to be not found and hence the JNIEXPORT and JNICALL also remains hidden.

build.gradle(app)

apply plugin: 'com.android.application'

android {
    compileSdkVersion 29

    defaultConfig {
        applicationId "com.karuneshpalekar.copencv"
        minSdkVersion 21
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags "-frtti -fexceptions"
                abiFilters 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a'
                arguments "-DOpenCV_DIR=" + opencvsdk + "/sdk/native"
            }
        }

        ndk {
            moduleName "test"
            cFlags "-std=c++11 -fexceptions"
            stl "gnustl_shared"
        }


    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild {
        cmake {
            path "src/main/cpp/CMakeLists.txt"
            version "3.10.2"
        }
    }

    packagingOptions {
        pickFirst 'lib/armeabi-v7a/libopencv_java4.so'
        pickFirst 'lib/arm64-v8a/libopencv_java4.so'
        pickFirst 'lib/x86/libopencv_java4.so'
        pickFirst 'lib/x86_64/libopencv_java4.so'
    }


}

dependencies {
    implementation fileTree(dir: "libs", include: ["*.jar"])
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.0'
    implementation project(path: ':java')
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'

}

build.gradle(java)

apply plugin: 'com.android.library'

println "OpenCV: " + project.buildscript.sourceFile

android {
    compileSdkVersion 29
    //buildToolsVersion "x.y.z" // not needed since com.android.tools.build:gradle:3.0.0

    defaultConfig {
        minSdkVersion 21
        targetSdkVersion 29
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_6
        targetCompatibility JavaVersion.VERSION_1_6
    }

    sourceSets {
        main {
            jniLibs.srcDirs = ['src/main/jniLibs']
            java.srcDirs = ['src/main/java']
            aidl.srcDirs = ['src']
            res.srcDirs = ['/build/master_pack-android/opencv/modules/java/android_sdk/android_gradle_lib/res']
            manifest.srcFile 'java/AndroidManifest.xml'
        }
    }
}

dependencies {
}

Thank-You for helping I have Ndk-rc21 and Android Studio AGP Version 4.0.1 and Gradle Versopion 6.1.1

The Issue I had was not with the NDK tool , it was with the directory where i had placed it.

There was space between file name which resulted in the error eg"User space Name".eg:C:/User/Elon Musk/SDK/ndk

I rectified this mistake of mine after a warning display by Android Studio lint .

I changed the Android SDK directory placement and rerun the code and the issue got resolved.

As per the answer above by Lakindu , there is no need for downgrading the Ndk library just make sure that the NDK is in the right place .

And also dont forget to add the NDK tool in the Project Structure which you can find by clicking Ctrl + Shift +Alt + S simultaneously.