Hello and welcome!
I’d guess that you did not generate the _NewEdit page or that the button does not have an action/is set to do nothing.
Here are some screenshots of the process in general
https://docs.mendix.com/howto6/create-your-first-two-overview-and-detail-pages
Hello, you can refer to this topic for a workaround
I would suggest taking a look to the Academy section and spending some time in the basics training.