Proper Video Settings Apple TV 4K

I have a Samsung Model 58" Class RU7100 Smart 4K UHD TV and I do not understand which video setting I should be using on Apple TV 4K. I tried 4K HDR but the picture was dark, so I switched to 4K SDR and the pic seems okay, but not sure whether to enable the frame rate & dynamic settings. I believe my TV is capable of HDR (per the book) - but yet as mentioned, the picture seems very dark at 4K HDR setting. Also, I see choices for 60 HZ and 50 HZ .. several other choices. I am at a loss as to know which setting to use.