Keynote: trying to add hyperlink, but no field to add the URL
After adding the hyperlink to the picture, if the dialog does not pop up, you can select it using the link icon (circle with arrow) that appears along with the picture.

Note: Be sure the picture is selected when adding the link.  ⌘+K

If this normal behavior is not happening for you, a restart of your Mac may correct it.



Illustration of how to bring up the dialog after setting the link: