I'm trying to boot my EVGA Z790 Classified with a Intel 14700k but keep getting a D6 post code. I tried updating to the newest bios which I guess was successful but the system is still not posting and going to the bios. I guess the bios update failed ? So now I'm stuck with a non-functioning motherboard that doesn't want to update the bios.
I don't really know what to do.

I'm honestly very frustrated with EVGA because they haven't released a new bios that is compatible with the 14th gen Intel cpu. This cpu has been out for over 2 months and still nothing from EVGA.

Update: Tried updating the bios without the 14700k in the socket and keep getting an e8 post error code when bios updating. Does anyone know what's going, this is getting ridiculous and I'm about to return the mobo for a refund.

I would return it asap. I don't think evga will ever release a new bios to work with the 14 series of CPUs. Its been months with people asking without a response from evga. 

Use a different board with the 14th series cpus. EVGA has made it clear that they will not be supporting the newer cpus.

Can't return the motherboard, it's past the return period so I contacted evga about a refund.

I tried booting the 14900K with my Z790 Dark with the same D6 code. They just don't work.

DreadNaught503
Can't return the motherboard, it's past the return period so I contacted evga about a refund.

You can sell it on any marketplace just be sure to tell people that you are selling it because it does not support 14th series. I don't think the product page lists 14th series support, so I doubt you can get any refund. 

GregorysBrain
I tried booting the 14900K with my Z790 Dark with the same D6 code. They just don't work.

D6 is video. Seems odd. Most people can boot 14900k on the evga boards, they just don't have all the voltage curves right (as it's the wrong microcode), but it should function. It's all the other 14th Gen skus that tend not to work at all. There's another thread where some folks were having luck getting it functional. Kingpin got his functional on z690 and Z790 too.

GregorysBrain
I tried booting the 14900K with my Z790 Dark with the same D6 code. They just don't work.

The 14900k works fine on my Z790 Dark, but not exactly 100% great voltage curve wise.

Installing an unsupported CPU will always be a hit and miss. I hope you are able to get your money back.