Similar story... I was holding out for a DDR5 build next cos my 6700K was still doing well enough. Then due to a lack of 3080s in shops was forced to buy a 3090, but it wouldnt work in my 6700K system (Maximus VIII Hero, 4x4GB Corsair LPX, Seasonic Prime UIltra Titanium 750W). On power up it gave an error code related to a memory problem and it would never post, no matter what was tried. The problem wasnt memory related, its still working fine in the same system +1080ti as I type this. So I built a gaming only machine for the 3090 with a 10700K CPU and faster ram. The ram from my 6700K system works fine in that machine, I never did suss why my old machine doesnt like the 3090. But damn, 6 months+ too early for the new machine!