How do I get the source code of my form?

The Source Code field (as in your description above) is not visible or available on my "Embed" page.

How do I get the source code then?

The source code embed is only available for Classic forms.

If you're using the Card Form this feature is not available.

You may try to embed the form using the Iframe code.

https://www.jotform.com/help/148-Getting-the-Form-iFrame-Code

Hope this information helps.