Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
@efil4ukoR Thanks for the notes here. Most channels (apps) on the Roku platform are developed and maintained by the channel provider themselves, including features & functionality, content availability, etc. If you have suggestions or feedback to share, we'd recommend contacting the support team of any channel provider directly to share your thoughts.
For example, the Disney+ channel only currently offers 4K HDR content on the Roku platform. The model of Roku TV you mentioned is an early 4K model which did not offer HDR. This is why you aren't seeing 4K HDR playback from that particular channel.
This is a disappointing non-answer. I've already tried Apple's support channels, and those refer me to Roku for an explanation. Both companies, Roku and Apple, are pointing the finger at each other, with their mutual customers caught in the middle. Appropriate staff at both companies need to talk to each other and see if these issues can be resolved. If the unfortunate reality is that some Roku devices will never be able to support Apple TV+, then the least customers are owed is a succinct explanation that Apple TV+ requires <insert name of specific capability> and the affected devices don't meet that standard.