One of the main changes for the 3.0 release is the Single Document Mode that has been improved.
This topic of having a “lighter” and simpler UI for JupyterLab has been discussed here on Discourse several times:
- Any recent usage polling on Jupyter Lab vs. Notebook usage?
- Benefits of the classic UI and use cases for classic over JupyterLab (Was: Why is Tim not moving to lab?)
- Deploying JupyterHub at your institution
So an issue has been opened to collect feedback: https://github.com/jupyterlab/jupyterlab/issues/9117