add in android/app/build.gradle:

android {
    .
    .
    .

defaultConfig {
    applicationId "com.app"
    minSdkVersion rootProject.ext.minSdkVersion
    targetSdkVersion rootProject.ext.targetSdkVersion
    versionCode 1
    versionName "1.0"
    multiDexEnabled true
    }
        .
        .
        .
   }

the line :

multiDexEnabled true

Can you try this bt=y adding

In your module level build.gradle file. Something like this:

android {     
  defaultConfig {         
  ...         
  minSdkVersion 21          
  targetSdkVersion 26         
  multiDexEnabled true     
 }     
... 
}

I get Execution failed for task ‘:app:mergeDexDebug’ when I install react-native-fbsdk 2.0.0 and then run react-native run-android.

My project with react-native:

 npmPackages:
    react: 16.13.1 => 16.13.1 
    react-native: 0.63.2 => 0.63.2

android/build.gradle:

buildscript {
    ext {
        buildToolsVersion = "29.0.2"
        minSdkVersion = 16
        compileSdkVersion = 29
        targetSdkVersion = 29
    }
}

console:

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:mergeDexDebug'.
> A failure occurred while executing com.android.build.gradle.internal.tasks.Workers$ActionFacade
   > com.android.builder.dexing.DexArchiveMergerException: Error while merging dex archives: 
     The number of method references in a .dex file cannot exceed 64K.
     Learn how to resolve this issue at https://developer.android.com/tools/building/multidex.html

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 11s

error Failed to install the app. Make sure you have the Android development environment set up: https://reactnative.dev/docs/environment-setup. Run CLI with --verbose flag for more details.
Error: Command failed: ./gradlew app:installDebug -PreactNativeDevServerPort=8081
warning: [options] source value 7 is obsolete and will be removed in a future release