sp-dev-fx-webparts/samples/react-rhythm-of-business-calendar/config/serve.json

{
    "$schema": "https://developer.microsoft.com/json-schemas/core-build/serve.schema.json",
    "port": 4321,
    "https": true,
    "initialPage": "https://contoso.sharepoint.com/_layouts/15/workbench.aspx"
}