First, perhaps understand the Apple Support Community is a user-to-user technical forum. Contributors here are all end-users, just like you. Other than the site Moderators, Apple neither monitor nor participate here. As such, if you hope to reach or receive a response from Apple via these forums, you will be disappointed.
Published specifications for the iPad A16 can be found here:
iPad 11-inch (A16) - Technical Specifications - Apple
The iPad A16 specifications state, as you correctly observe, support for HDR10 video playback. Key words here are "support for". Ultimately, the both the App used for playback (in this case YouTube) - and the source video material - must also be HDR10. In summary, the iPad hardware does support HDR10, but can only display HDR10 material if the App and streamed content are also using this video format.
If you are experiencing issue with the YouTube App or video content, you will need to seek assistance via the YouTube online help resources.