Question about Apple TV 4K (3rd Gen) + Ethernet

Hello, I have had this Apple TV product since Christmas and am very satisfied. However, the volume control including the mute button does not work. I initially thought it was because I stream on Netflix and these buttons may only work for the Apple TV streaming provider. I then did some research and found out that these buttons should always work in every app. I then tried all the tips from people with the same problem, but couldn't solve the problem. Can anyone help me or is the product defective?