The be quiet riser cable is designed for PCIe 4.0 graphics cards and does not directly support PCIe 5.0 or specific models such as the RTX 5090. It is not clear whether it is compatible with PCIe 5.0 graphics cards, as this technology is not explicitly supported. For the RTX 5090, it would be advisable to check compatibility directly with the manufacturer, as the information on this is not complete.