sp-dev-fx-webparts/samples/react-private-libraries/config/serve.json

{
    "$schema": "https://developer.microsoft.com/json-schemas/core-build/serve.schema.json",
    "port": 4321,
    "https": true,

    "serveConfigurations": {
        "default": {
            "pageUrl": "https://russellwgove.sharepoint.com/sites/ReactPrivateLibraries/_layouts/15/workbench.aspx"

        }
    }
}