[Tomte]

Does debugging work for you?

Neither in Notebook nor in Lab can I click in the gutter to set breakpoints. The debugging panel is open, the documentation is clear (except that by default there are no line numbers and you have to activate that), but nothing happens.

Where exactly am I supposed to click?

[afshin]

There is a little bug icon in the toolbar of your open notebook in both user interfaces. The bug only appears if you have a kernel that supports debugging (e.g., ipykernel). So if you see the little bug on the right-hand side of the toolbar for your notebook, when you enable it, you should start seeing the variables in your memory state and you should have the ability to click in the gutter to add breakpoints.