TV Model - Q60T
I can play two 4k shows via Netflix on the tizen app, both show as 4k on Netflix, but only one will show "HDR" when going to the picture mode settings while watching. For example "Our Planet" it shows HDR in picture mode setting, while "Grace and Frankie" does not. My understanding is the quickest way to confirm what you selected is actually showing in 4k is to look at picture mode and confirm that it says "HDR" there.
Additionally, any show I've tried on Amazon Prime or Hulu (even on Roku instead of tizen native Hulu app since I know hulu doesn't support 4k on tizen hulu app) doesn't show "HDR" on picture mode either.