An AIO liquid cooled GPU. The weight of the radiator is not supported by the PCIe slot, but total weight, it is probably the heaviest The AMD R8 285 X2 for example -- https://www.theregister.com/2014/04/08/amd_unveils_radeon_r9_295x2_dual_gpu_graphics_card/one of the super over engineered 3090 cards would be my guess.
This, my 3080 ti suprim x, weighs exactly 2 kilos or 4.4lbs lol, thank god it came with a supportive standLikely what Math Geek said. If not a very overengineered 3090 with a cooling apparatus strong enough to cool video cards upcoming for the next decade and heavy enough to prove it, it would be a 3080Ti or 3080. Some of the coolers on those 2 models too get very righteously overengineered and heavy too. Out!