You have to do a search having both of the use miles and flexible dates selected which pops up the calendar search. That is the old site, and then you can unselect the use miles box and select the nearby airport boxes. As I said, it's a pain but the old site works better. Flexible dates/calendar search never allowed nearby airports.

Also to add, mobile site (which now looks the same) doesn't work. You have to request the desktop site in the browser, or just use a desktop, in order to select both of those boxes initially.