"The jupyter notebook looks completely different. Can anyone help me on how to get back to the original one?"
To address the second question quoted, you are looking for NbClassic. The developers have made that the way to keep the older style interface.
From the NbClassic repository:
"NbClassic provides a backwards compatible Jupyter Notebook interface that you can install side-by-side with the latest versions: That way, you can fearlessly upgrade without worrying about your classic extensions and customizations breaking.
How does it work?
Because NbClassic provides the classic interface on top of the new Jupyter Server backend, it can coexist with other frontends like JupyterLab and Notebook 7 in the same installation. NbClassic preserves the custom classic notebook experience under a new set of URL endpoints, under the namespace /nbclassic/."
More about that and the answers to your first questions are covered by looking into the following resources that discusses recent developments in regards to the interface options for editing and running .ipynb
files in the Jupyter ecosystem.
More on Jupyter ecosystem, an overview:
https://twitter.com/jtpio/status/1683399787876429825 July 2023
"Our talk with @JohanMabille on Navigating the Jupyter Landscape is now available on YouTube 🎦 🎉
Check it out if you want a high-level overview of the Jupyter ecosystem and learn more about the underlying projects and libraries.Jeremy Tuloup, Johan Mabille Navigating the Jupyter Landscape | JupyterCon 2023"