It's sad looking at the Q&A on the product page where the Dell reps don't even have an understanding of what PCIe slots are used for.  

If the photo on the web site is that of the Nvidia 4080/90, it seems like 1 slot (at the bottom) might be usable? The new AMD offering specs out at 2 1/2 slots (instead of 3 for the Nvidia) but I don't know if that would reveal the upper PCIe slot for use or not.