1 x pcie 4 0 x16 slot ✓ Will PCIe x1 x4 cards work in x16 slot?

1 x pcie 4 0 x16 slot
The number '4' after 'x' denotes how many PCIe lanes the slot has Most of the time1 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?

1 x pcie 4 0 x16 slotExpansion Slot 1x PCIe x16 slot ; 2x PCIe x1 slots The supported specification depends on installed processor Onboard Graphics 1x VGA

1 x pcie 4 0 x16 slot 4 slots x16) with the latest AMD or Intel processors support? slots and one x1 slot There