Netflix says that it is enabling HDR10+ with the AV1 codec that was released in 2018. This codec was originally adopted by Netflix to lower the amount of data customers use when streaming 4K content on phones. But the codec works just as well on large HDR files.

Netflix has started streaming shows and movies in HDR10+, finally supporting the video format that improves picture quality for users with compatible devices. In a nutshell, HDR10 uses static metadata,

Netflix has revealed that it’s just added a new feature to its film and TV show streaming service that should instantly improve picture quality for millions of its subscribers around the world. This new feature is support for the HDR10+ high dynamic range video format;