https://en.wikipedia.org/wiki/... is new but the idea goes back decades.
""mutual aerial observation" was initially proposed to Soviet Premier Nikolai Bulganin at the Geneva Conference of 1955 by President Dwight D. Eisenhower"
So the use flights can have "video, optical panoramic and framing cameras for daylight photography, infra-red line scanners for a day/night capability, and synthetic aperture radar for a day/night all weather capability" with 'Imagery resolution is limited to 30 centimetres".
So what can been seen helps "enhance mutual understanding and confidence by giving all participants".
"international efforts to date promoting openness and transparency of military forces and activities" is another way of saying counting what is out in the open.
Tanks in rows, aircraft parked, sites of interest. An old idea, many normal flights other the years by different nations. Nothing really new or interesting since the 1990's for Open Skies.
Lots of nations also use the international airspace for complex spy flights as they have done since the 1950's.