possible to split a PCIe slot?

The X570 TUF does not come with an X4 slot and I'm not sure if I'll be using the second PCIE X16 slot for something else 4x card directly at

PCIe boards can fit into slots designed for their lane configuration or higher Plugging a x4 PCIe into a x16 slot is acceptable

4x4 mega slot PCIe Slots PCI Express replaced AGP and PCI as it is faster than PCI Express 4x, 1600 MBs PCI Express 8x, 3200 MBs PCI Express 16x, 6400 MBs

4x4 slot Both run 1x on the 4x slot