The Apple TV 4K will play all Dolby Vision content in HDR10. It will also change the label of all Dolby Vision content to HDR10. The TV apps will also play Dolby Vision content in HDR10. There is some content available from Amazon Prime Video and Hulu in HDR10+ and the TV will make use of it.
Remember that HDR10 is the default HDR format in every HDR capable device and will be output when devices do not support Dolby Vision or HDR10+. So, all Dolby Vision content from the Apple TV 4K will make use of HDR10 when connected to a Samsung TV.
Samsung Smart TV apps will make use of HDR10+ when available to them from their built-in apps or from supported services in devices such as the Roku Ultra or Google Chromecast with Google TV. Any receivers between such devices and the TV need to support HDR10+ as well.
Passing Dolby Vision and HDR10+ is not just a hardware issue. If streaming services do not support them, then it matters not if the equipment supports them. Some free trial and lower tier subscriptions to some services do not support HDR of any flavor. And, even if they do support it, they may not support it on certain TVs and devices. It’s a jungle out there.