Week 4, exercise 1, "Submit" button does not show anymore

Yes, that is the problem. You can see in the first image that you posted that you are using the renamed saved version of your previous work. That doesn’t work. The point is that your notebook got renamed because the course staff published a fixed version of that notebook. You could just rename your saved version back to the “official” name, but then you miss out on the fixes. The only real solution is to open the new clean version with the fixes and your saved version in parallel and then carefully “Copy/Paste” over your completed code into the new notebook.

And BTW this whole mess is described in detail in a topic on the FAQ Thread. See the topic about “Help! My work disappeared!” There’s also a topic about “No submit button”, which covers the point that Tom made about needing to use the “official” name of the notebook.