...rather than repeat everything about what I just posted here (primarily on the RTX 3K supply), I add that so far, I have only seen GN's and a few other 6900XT reviews, and beyond that expect the supply issues to be similar.
What's more, AMD's bios and driver team don't seem to have been ready yet @ release of the 6900 XT. It may very well be a good card, but I do think that the 4K constraints via VRAM bus and also ray tracing / DLSS are NOT 'unimportant'.
I was / am rooting for the 6900 XT. What really disappoints me though is where I have a lot of background, and that is MS FS 2020 (currently DX11) compared to the 2x 2080 Tis I run at 4K / ultra...neither the RTX 3900 nor the 6900 XT would tempt me in the slightest on that.
But leaving all that behind, there's another big issue...over the last several years, PC sales (including many components) were flat to slightly down-sloping, due also to the rise of smart phones, tablets and consoles, if one believes the analysts' reports. Yet now, there's this giant opportunity posed by Covid-19 via a lot of folks spending way more time and home (work and play) and discovering that their ancient PCs really should have been upgraded years ago, both for productivity and entertainment...only they can't get any decent supply of any new higher-end stuff...
..yes, vendors may not be at fault, given the dearth of what's coming down the pipeline from the foundries on the higher-end into vendor sales channels. But really, after all these years, this turns out to be an inflexible industry when facing with a big gift-wrapped global opportunity