HDR10+

Apple TV 4K currently supports HDR10 and Dolby Vision — not HDR10+. But HDR10+ content is backwards compatible with HDR10, so you should still get some high dynamic range effect.

Apple TV 4K (1st generation) technical specifications - Apple Support

Apple TV 4K (2nd generation) technical specifications - Apple Support

What’s new in tvOS 16 - About Apple TV 4K and Apple TV HD software updates - Apple Support

Also be aware that only major two brands of TVs support HDR10+ at this time, Samsung and TCL. So even if you have the new Apple TV and play HDR10+ content it won’t make any difference unless you also have a Samsung or TCL TV to display it. Samsung’s reasoning is that it refuses to pay the licensing fees for Dolby Vision, the most popular version of HDR right now. Samsung is also the co-creator of the HDR10+ format along with Panasonic.

Unfortunately once again it’s become a pi**ing contest between manufacturers with Samsung and Amazon Video pushing HDR10+ while Sony, Apple, LG, Toshiba, Vizio are pushing Dolby Vision. All of Apple TV+ content is Dolby Vision.

Some TVs support both.

A new generation Apple TV box has been announced, and it features HDR10+. It seems you will have to buy new hardware to get that.

It was announced by Apple at one point, but any mention was a little later removed by Apple. Not sure why.