Missing Build settings in AWS Amplify Hosting for Flutter Web Apps deployment

You will need to build your backend and frontend. For my amplify backend I'm using typescript so I need to install typescript in the preBuild phase.

For the frontend you will need to install flutter and then build your app. My build command is in a Makefile, but something like flutter build web --release should work

version: 1
backend:
  phases:
    preBuild:
      commands:
        - npm install
        - npm install -g typescript
    build:
      commands:
        - '# Execute Amplify CLI with the helper script'
        - amplifyPush --simple
frontend:
  phases:
    preBuild:
      commands:
        - npm install -g gulp
        - yum install -y xz
        - curl -LO https://storage.googleapis.com/flutter_infra_release/releases/stable/linux/flutter_linux_3.16.2-stable.tar.xz
        - tar xf flutter_linux_3.16.2-stable.tar.xz -C /usr/local
        - export PATH="/usr/local/flutter/bin:$PATH"
        - git config --global --add safe.directory /usr/local/flutter
    build:
      commands:
        - make build
  artifacts:
    # IMPORTANT - Please verify your build output directory
    baseDirectory: build/web/
    files:
      - '**/*'
  cache:
    paths:
      - node_modules/**/*