Insert/overwrite shortcut key in Jupyter

For me fn + insert solved the problem.

Finally tracked down the problem: it was a Linux one to do with enabling Numlock. As Numlock was not turned on, the 0-key on the number keypad was acting as a toggle for insert mode.

To turn on Numlock, I had to install numlockx and then change login window preferences to enable it, e.g. see https://unlockforus.com/numlock-linux-mint/.

FWIW, on a Macbook running Linux, fn + return toggles insert mode.

The Insert key on Linux should toggle it.