Airflow 2 supported Flask Appbuilder views (appbuilder_views), Flask AppBuilder menu items (appbuilder_menu_items), and Flask Blueprints (flask_blueprints) in plugins. These have been superseded in Airflow 3 by External Views (external_views), Fast API apps (fastapi_apps), FastAPI middlewares (fastapi_root_middlewares) and React apps (react_apps) that allow extended functionality and better integration with the Airflow UI.
https://airflow.apache.org/docs/apache-airflow/3.1.8/administration-and-deployment/plugins.html#flask-appbuilder-and-flask-blueprints-in-airflow-3
