Is there a way for two People to work on one Jupyter Notebook

CoCalc is expensive.

Fortunately, we also provide a complete free easy to install open source version of CoCalc, which you can run on any computer that supports Docker. For example, here's how to run it on Google cloud.

(I have put too many years of my life into making realtiime collaboration work for Jupyter via CoCalc... In any case, the open source code has been battle tested in production for a while now and is working well finally. I hope it can solve your problem...)

You can upload your notebook to Deepnote. It provides a hosted environment, where you and your colleague can connect at the same time and work on the same notebook in real-time (the same way you'd do in Google Docs).

Colab is also good, but writing at the same time will result in conflicts.

Notebook itself doesn't support to collaborate simultaneously, but you can use GitHub to manage your python script and upload it into Colab separately. This way Github can help manage the file history and solve the conflicts.