In earlier versions for the page resource there was a drop box given to chose embed , pop up automatic option . The option exists for files. How ever for the page section this option is missing. Is it a bug??
Have you looked in Settings>Site admin>plugins>activity modules>Page?
Thank-you for posting this tip.
FWIW: If a course containing a Page with 'Display: popup' set is backed up/restored to a site where the setting is NOT yet enabled, the page will continue to display that option.
(I was mystified as to why that setting wasn't showing on my new pages.)