The OptiPlex 7090 SFF has three slots but watch the PCIe wiring
One PCIe x16 slot (physically x16, electrically x4 only), one PCIe x4 slot, and an M.2 2230 key E slot for Wi-Fi. That x16/x4 gotcha limits GPU options — stick with low-power cards.
One PCIe x16 slot (physically x16, electrically x4 only), one PCIe x4 slot, and an M.2 2230 key E slot for Wi-Fi. That x16/x4 gotcha limits GPU options — stick with low-power cards.