Don't own the mu6103 but....
If i remember correctly, You need a minimum of 25Mbps to get UltraHD 4k / HDR contents from netflix.
If you're browsing your netflix app through the tv there should be an Ultra 4k category. if it doesn't show up then your internet speed is not fast enough.
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Googled it:-
Netflix supports two different HDR streaming formats, Dolby Vision and UltraHD Premium (HDR).
What You’ll Need:
A TV that supports either Dolby Vision or HDR and Netflix. (If you use a set-top box to stream Netflix, both the set-top box and TV must support HDR.)
A 4 Screen Netflix plan. You can check which plan you're currently on at Netflix.com/ChangePlan.
A steady internet connection speed of 25 megabits per second or higher.
Streaming quality set to High. More information about video quality settings can be found in our playback settings article.