motherboard 6 gpu slots
How Many M.2 Slots Do Motherboards Have? - PC Guide 101
The 3500X only has 20 PCIe lanes of bandwidth, so onboard devices on the motherboard, and your GPU using them up, could be limiting the M.2_1 slot to x2.
Mini PC NUC ASUS INTEL NUC 13 Pro ( Core i3-1315U | DDR4 3200 ...
Buy ASUS Prime Motherboard B660M-A WiFi D4 LGA 1700(Intel 12th Gen) mATX (PCIe 4.0, Wi-Fi 6,DDR4,2xM.2 Slots, 1Gb LAN, DP,2 x HDMI, USB 3.2 Rear Gen 2 and ...
List of Motherboards with 2 RAM Slots
This micro-ATX Gigabyte motherboard has four SATA 6Gb/s ports and a single M.2 slot. Like any other basic A520 chipset, it doesn't support dual-GPU.