I have a Samsung OLED TV that plays sound when using my Bose Bluetooth headphones. Couldn't turn the TV sound off no matter what I tried. Went to settings / accessibility / paired devices and saw my headphones and my Samsung soundbar listed as paired even though the soundbar is optically connected to my TV. So I went back to Settings / Sound Output, selected the soundbar and sure enough, it's volume was at level 6. I then ran the soundbar volume down to 0 using the soundbar remote and the problem was resolved.
