My 49SK8500 also had the pop-up when I switched it on the other day. I had a flick through what's available on Apple TV+ and decided to watch the free episodes of Ted Lasso, which are pretty funny (and it's fun spotting locations like the pubs and alleyways of Richmond).
The TV recognised that the show is in Dolby Vision and switched to Cinema Home mode, and some of the shots displayed that extra 'pop' that you get with HDR. However I felt that the picture was fading from brighter to dimmer in some scenes. Is this a feature of Dolby Vision or an error in the TV? Is there a setting that needs to be changed to stop this happening?