I also reported today via Feedback to Lenovo, that HDR playback on China FW is actually broken, instead of black color you see gray... HDR10+ and Dolby vision is OK ... this was the main thing why I invested in this tablet and of course it's broken... just my luck... oh, well... hope global FW don't have this bug and I find soon how to flash it...
I can confirm that i do also have issues with HDR in the global version (Build number TB132FU_S000073_220816_ROW), but only in the YouTube App (and also YT Vanaced).
But if i play the HDR video files with another Player (Plex for example) HDR, HDR10+ and DolbyVision works flawlessly without any issues.