What settings are you using on the TV itself? I just the other week I got a 50" 6 series samsung 4k with HDR and a lot of advice online is to set the TV to game mode, turn off the motion smoothness options and make sure hdr colour is enabled on the hdmi ports in the tv, these settings are under external devices manager under the main general tab. There is a black level option too which sometimes I change from standard to low depending on game/movie it also suggests to disable all eco power saving features. And finally the device you tell your tv it is connected to should NOT be PC, you should tell the tv that it is a blue ray player, so select that as the device and just rename it, this is to make sure the TV works properly with HDR content.
If you want to view 4k HDR video content you're going to have to buy and download a codec from microsofts store called HEVC, costs about a quid and you need this to play videos through media player classic but more importantly through apps that have 4k and HDR capability, mainly Netflix so far and some support is enabled in the edge browser, you have to use this codec because it has built in digital rights management (DRM). But yeah you need it if you want 4k HDR in the Netflix app and you'll need a premium netflix account to get 4k and HDR enabled streams and you have to go to their site and change the speed setting to high. You can confirm its working by watching stranger things and before playing the video, in its info you will see a box with HDR, if you see only 4k you've not got HDR working properly so check to see if you enabled it in display settings in windows there is a slider switch to enable HDR and wide colour gamut.
Below is a link to a video that's 4k HDR enabled, if this plays with sounds and a beautiful crisp image with vivid colours then you're good to go, if the colours are super over saturated make sure you've enabled the HDR option in wondows10 display settings. The Tv should go black for a second shortly after the video starts, thats the indication its switched itself into HDR mode. If no video plays, you've not installed the codec.
Some final points, you're using a 9 series card going by your sig and they dont fully support HDR I've not read much about it but it is possible for it to work if you have it connected with a HDMI cable that is 2.0/18GBs compliant. I'm basically new to all this myself and it's convoluted, you may have better results with different settings to mine especially as you're on a newer more colour capable board, I have some issues when enabling HDR in windows 10 that it makes the display in non HDR settings look washed out, I counter this by only enabling HDR when using it, games seem able to enable HDR mode even if it is not enabled in the windows 10 display options. I think because this is not a fully adopted standard, the software with MS and nvidia isnt as good or compatible as it should be yet. Might be worth googling your TV and look at how others have used theirs as PC monitors. You may not get the washed out issues at all because the HDR in your tv I think is a more fully compliant version of HDR10 compared to mine, will be interesting to hear if you do or not.
Hoped this helped a bit because it's a right bollock on, I know not specifically about the issues you mentioned but maybe they will have some affect on it.
Codec;
https://www.microsoft.com/en-gb/p/hevc-video-extensions/9nmzlz57r3t7?activetab=pivot:overviewtab
4K-HDR-Video test file .ts format ;
https://drive.google.com/uc?export=download&id=0Bxj6TUyM3NwjWnNqSnNoSElndDg
