Flutter: How to fix “unexpected element found in ” error?

 All of a sudden, I am started getting this build error in my Android project:

Error: unexpected element <queries> found in <manifest>

Understanding  the Issue:

To understanding why this happens see the above @CommonsWare's answer

This is because <queries> tag was introduced with new package visibility options for Android 11 and upwards (SDK 30+). Because of that, you need to update your build.gradle with a version that includes this changes. Below is a list of supported gradle options.

The best solution to deal with these errors is to Upgrade your Android Gradle plugin and Update Gradle

You’ll have to update your Gradle version to one of the compatible versions that have the latest query tags (which were introduced with Android 11).

How to Fix it?

To Update the Android Gradle plugin

Specify the plugin version in the YourAppDirectory/android/build.gradle file. The plugin version applies to all modules built-in that Android Studio project. The following example sets the plugin to version 4.0.1:

buildscript {

    ext.kotlin_version = '1.3.50'

    repositories {

        google()

        jcenter()

    }

    dependencies {

        classpath 'com.android.tools.build:gradle:4.0.1'

        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"

        classpath 'com.google.gms:google-services:4.3.3'

        classpath 'com.google.firebase:firebase-crashlytics-gradle:2.2.0'

    }

}

Gradle downloads it the next time you build your project 

To Update Gradle

Specify the Gradle version by editing the Gradle distribution reference in the YourAppDirectory/android/gradle/wrapper/gradle-wrapper.properties file.

Don't forget to update your ditributionUrl in your gradle-wrapper.properties as well. For example, for gradle 4.0.1, you should have:

#Fri Jun 23 08:50:38 CEST 2017

distributionBase=GRADLE_USER_HOME

distributionPath=wrapper/dists

zipStoreBase=GRADLE_USER_HOME

zipStorePath=wrapper/dists

distributionUrl=https\://services.gradle.org/distributions/gradle-6.1.1-all.zip