I have a new 2018 TCL 55R617 and when I use the Roku iPhone app to control the picture settings I cannot select HDR Dark. I am able to select other modes such as Vivid, but none of the HDR modes. When I try, it simply states "Operation Error" and to try rebooting... which I have.
This is supposedly a known issue with Roku App. I have been complaining about this for months now and they wont tell you anything except they are working on it. It's actually a disgrace. I think they know about the issue but refuse to fix. It's an APP issue. I get that to. It's not your tv so don't worry about it. If you complain they will just say they are working on it with no fix in sight. Sorry man. I have a droid phone so you just confirmed that its happening on iPhones to. Thanks for that piece of information..
@jobiegermano Thanks for reaching out! This is an issue that our team is currently looking into, as referenced above. In the meantime, you can still use your Roku TV remote to adjust these settings during content playback by pressing the * key on your remote to open the settings menu 9n the left-hand side of the screen.
We'll continue to keep everyone informed when we have any further updates to share.