Right: the IPython- and Jupyter-APIs are not available in clients other than notebook <6, e.g. JupyterLab, VSCode, Colab. It is also uncertain whether these will be introduced as shims in notebook 7.
JupyterLab, in specific, offers an --expose-app-in-browser option, but that API (jupyterapp) is different, and limited in its own ways.
ipylab provides some options for bridging some of these gaps, but is then more tightly bound to that client.