This was a little tricky, since flask by default runs on localhost as 127.0.0.1. That’s not visible outside the container so the ‘lunach.json’ needed to be …

{
  // Use IntelliSense to learn about possible attributes.
  // Hover to view descriptions of existing attributes.
  // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Python: Flask",
      "type": "python",
      "request": "launch",
      "module": "flask",
      "env": {
        "FLASK_APP": "app.py",
        "FLASK_ENV": "development",
        "FLASK_DEBUG": "0",
      },
      "args": [
        "run",
        "--host",
        "0.0.0.0",
        "--no-debugger",
        "--no-reload"
      ],
      "jinja": true
    }
  ]
}