The key difference in the ‘new’ list is there in line with your title:
Notebook 7+ is built on top of JupyterLab components and so it is more modern and has additional features & abilities. The developers have endeavored to keep the same functionality; however, sometimes it is accessed in different ways than before and some of the functionality is still being made to be consistent.
If you want the older interface, you are looking for NbClassic.
@Edifon_Jimmy This is almost certainly unrelated to the new version of Notebook, but to the version of packages (seaborn/matplotlib) that you have installed or differences in the code being executed. Notebook does not control the details of plot outputs.