Can You Use a PCIe Express Card In a Slot?

You can buy a PCIe expansion card but have a motherboard with PCIe slots, for example Thankfully, PCIe is backward compatible, so

Each PCIe3 6-slot fanout module provides six full-length, full-height, PCIe3 slots The PCIe3 slots are compatible with PCIe1 and PCIe2 adapters

pcieslot  PCIe x16 5 x PCIe x16 4 x PCIe x16 3 x PCIe x16 Power Phase, Chipset, Memory, Slots, Multi-GPU, Graphics, Audio, Network

pcie 4 nvme in pcie 3 slot Most commonly, PCIe expansion slots are used for the add-in graphics card, SSD storage devices, Wi-Fi adapters, and other sorts of expansions