The Apple TV app on third-party devices such as Samsung TVs has been updated to support HDR10+ streaming for both TV+ titles and iTunes movies.
Apple recently announced HDR10+ support in the Apple TV app, but then removed all references to HDR10+ again.
The announcement was premature but HDR10+ has now begun to roll out in the Apple TV app on Samsung Smart TVs, according to multiple users (1, 2, 3).
iTunes movie rentals and purchases such as Top Gun: Maverick as well as Apple TV+ titles such as Ted Lasso are available in HDR10+. This suggests that Apple is adding support for HDR10+ across the content library as a third HDR option in addition to base HDR10 and Dolby Vision. However, the film studio must provide to Apple an HDR10+ master file and only a handful of studios release content in HDR10+.

The Apple TV app now supports three HDR formats: HDR10, HDR10+ and Dolby Vision
Like Dolby Vision, HDR10+ uses dynamic metadata to improve the HDR picture on a scene-by-scene basis. You can see which TV models support HDR10+ in FlatpanelsHD's TV Database by using the HDR10+ filter.
Apple will next week launch its third-generation Apple TV 4K that also features HDR10+ support.