With the latest Open Beta 3 update for OnePlus 7T series, among other new features and fixes, there is a new 960fps slo-mo mode in the video, previously which was 480fps. OnePlus quietly added this new video mode and did not mentioned in the changelog of the update. It means the Snapdragon 855+ is very much capable to handle 960fps.
Another new feature has been included is the 4K video recording using the ultra-wide cameras on both 7T and 7T Pro. All these features were discovered by a Reddit user sneakerspark, He posted this on the sub Reddit of Android. It is nice to see that OnePlus is including new features where the hardware is not a problem in terms of power and capability. These new features will come to official builds in the near future.