What firmware do you have on both TV and receiver? Yamaha should provide an update for earc for both 70 and 80 series, maybe you got that already? I just don't believe in miracles
So I have tried a cheap Denon receiver with the TV, nothing. Denon support says that DD+ over ARC works but I coudn't get more than DD (which works very well with the Yamaha too). Returned the Denon and unhappy so far with Samsung support, John Lewis finally sent an engineer which could again only see the issue. No new hardware brought to test this further.
They're going to change the main board and, I have been told, use some firmware that it's not accessible to public. My expectation is that it's not going to change anything.
But please, welcome the world of cheap and working TVs. My "new" Hisense cheap TV works with Netflix and DD+: https://youtu.be/lIZz8mmo4kY. So, dear Samsung, a 1300 pounds Yamaha receiver doesn't support DD+? Very true, just with your 1300 pounds TV perhaps., but it works with a TV that costs less than 300 pounds. Happy days.