extra pcie slots: Mini PC ASRock DeskMini X300 - X300/B/BB/BOX. Dell PowerEdge R720XD 3.5" Rackmount Server. What is PCIe x1 slot used for? - stc-cable.com.
PC Mini Asus PN63 Barebone (i5-11300H, Wi-Fi 6, BT5.0, Vesa Mount, VGA port) ...
Slots: 1 PCIe 4.0 slots, 3
PCIe 3.0 slots & 1 M.2 PCIe 3.0 x2/SATA
slot.
RAM support: Up to 288GB (18
DIMM slots): 1GB/2GB/4GB/8GB/16GB DDR3 800MHz, 1066MHz, or 1333MHz.
I/O Slots: 2 PCIe x8 + 2 PCIe x4 G2 or 1 x PCIe x16 + 2 PCIe x4 ...