the title is a bit missleading, so let me explain my setup.
I've got an intel NUC7i3bnk hooked up to an Onkyo TX-RZ710 receiver. This, in turn, is hooked up via a 20-25ft HDMI active cable, that in turn is hooked to a wall jack. The wall jack has a CL2 HDMI 2.0 (18Gbps) cable that runs through the walls + ceiling to another wall jack behind the TV, which in turn has a 3ft HDMI cable hooked to an LG OLED 65" B7A tv. When I had a Samsung 1080p TV on the wall, there was no issue at all playing videos (I use Plex Media Player embedded on the NUC). As soon as I replaced the TV, The NUC would refuse to display video on the tv. At first I thought it was my receiver (I had a TX-NR636 before), so I replaced it with a more modern one, but this didn't improve things. Then I thought that it might be the HDMI cables (shudder at the thought of replacing the one in the ceiling/walls), so I grabbed my work laptop and plugged it into the end of the cable coming out of the Onkyo (so as close to the NUC as possible), and TADA! i get 4K video out from my laptop, so I know it's not the cable from the Onkyo -> wall -> ceiling-> TV. This led me to deduce it was the NUC, except for I then tried to plug the NUC directly into the TV, and guess what? It worked.
So now I'm baffled. I'm running the latest BIOS 0057, as well as I believe 1.66 HDMI firmware (I see a 1.72, but it's a pain for me to update it since I'm running embedded PLEX player, woudl have to reformat with a win10 trial). It would seem to me that the NUC is having some sort of handsake issue, but I can't explain it. I've tried both HDMI and using a USB-C to hdmi adapter, I get absolutely ZERO video when I have the NUC take the "long way" to the TV. I'm still convinced it's some sort of handshake error, but I can't explain it. Again, the nuc worked fine with a 1080 TV, but as soon as I went native 4k, it suddenly is having problems.
Does anyone have any ideas?