https://flutter.dev/docs/deployment/android see the doc for reference

Signing the app:

To publish on the Play Store, you need to give your app a digital signature. Use the following instructions to sign your app.

Go through the screenshots below carefully to understand how to generate key and and use it for the released signed app:

Setup environment for keytool:

1. Run this command in your system terminal: flutter doctor -v

2. Find the Java binary at: copy this path except the “java” folder.

3. Change your terminal path by running this command : cd “past here your copied path” then press enter. Example: cd C:\Program Files\Android\Android Studio\jre\bin 

4. Run the keytool.exe file. Example: C:\Program Files\Android\Android Studio\jre\bin>keytool.exe

Create jks file for uploading app on playstore:

1. Open your project path and run this command: keytool -genkey -v -keystore android/app/key.jks -storetype JKS -keyalg RSA -keysize 2048 -validity 100000 -alias key 

2. Provide all information.

Your created JKS file is located your project->android->app folder

** If you lose the jks file , you will not be able to release a new update your app in playstore**

Enter the information in the file key.properties in the android folder.

1. storePassword.

2. keyPassword.

3. keyAlise.

4. storeFile

Read this

in app/build.gradle  do necessary changes

Note: You may need to run flutter clean after changing the gradle file. This prevents cached builds from affecting the signing process.

Now you are almost done

In your terminal run : flutter build appbundle

The release bundle for your app is created at <your app dir>/build/app/outputs/bundle/release/app.aab.

Upload this app.aab file to your google play console