Ok that is very recent, I see it mentioned this week also in this articleAccording to Engadget review, the answer is yes, Apple TV+ content supports HDR10+ content now.
Full review here.

Apple TV app on smart TVs now streams in HDR10+ | AppleInsider
Apple has rolled out an update to its Apple TV app used by smart TVs and other devices, bringing HDR10+ support for Apple TV+ streams and for iTunes movies.