Only Samsung can fix this. I have seen APPS change volume but they do so in the player and not in the actual TV to Bluetooth or Optical feed.
It's all pretty technical and I decline to write why this is as it's been done to death on the Internet.
If you feel the product is defective, use that as your reason to go get a full refund and begin the search for a TV that works for you.
When I pair my Samsung UHD Smart TV (model UE49KU6452U) with a bluetooth receiver, I'm not able to use the TV remote control to adjust the output audio volume.
The TV is able to pair but fails to adjust the audio level with both bluetooth receivers that I own:
* Sony WH-CH700N bluetooth headphones
* Logitech Bluetooth Audio Adapter (Amazon choice) - connected by cable to sound speakers
But I'm able to pair and adjust the audio volume of both these receivers from all other equipment that I have:
* iPhone 8
* MacBook pro mid 2015
* HP laptop running Windows 10
I also had friends pairing different mobiles (android, iPhone) with these receivers and it always works with no problems. Only the TV fails to do it.
Searching the web I find lots of people having the same problem with Samsung TVs (multiple models - or maybe all?) but no solution so far.
Is Samsung able to release a firmware update to fix this issue/bug?
It should be doable over software because on the following scenario:
* TV is paired over bluetooth with one of the receivers
* I cast youtube from my mobile to the TV
adjusting the audio volume through the youtube app interface on my mobile - works! It shows a different audio bar adjusting on the TV screen and successfully adjust the output audio volume on the receiver/headphones.
This proves that the TV can adjust the audio volume over bluetooth - It's not a hardware limitation, only software/firmware limitation.
I already tried to contact Samsung support and retailers to no avail... hope CNET is the one to finally provide a solution and answer to this issue.