1 x pcie 4 0 x16 slot ✓ Will PCIe products be compatible with existing PCIe , PCIe

1 x pcie 4 0 x16 slot
Biostar ; 2, 4 x DIMM DDR5-6000+ up to 192 GB Memory ; 3, 6 x SATA III Connectors ; 4, 1 x PCIe x16 Slots ; 5, 2 x PCIe x16 Slot ; 6, 2 x PCIe1 x pcie 4 0 x16 slot AMD TRX40 E-ATX motherboard sTRX4 for 3rd Gen Ryzen Threadripper, with 16 power stages, PCIe , Wi-Fi 6 , 10 Gbps Ethernet, Gen2x2

1 x pcie 4 0 x16 slotThe slot is physically 16x so a 16x card like a gpu will fit in it but only 4 lanes are wired so the card will run at 4x speeds

1 x pcie 4 0 x16 slot 1 x PCIe x16 slot I understand the first bullet point, but Why does a PCIe slot which has only 4 lanes physically has 16-slot size?