Yes, you can install a 1x PCIe card into a 16x or 4x PCIe slot

Design Ready for PCI Express 1*PCIe x4 & 2* PCIe x4 with Thermal Guard; 1*PCIe x16 with Ultra Durable™ Armor; 2*PCIe x1 5

This PCIe x1 to PCIe x16 Slot Extension adapter provides enhanced compatibility between motherboards and a variety of PCI-Express expansion cards, allowing you

1 slot gpu It does include a PCIe x16 slot, but rather than a second one, like Asus did with the E Gaming, it offers not one, but four PCIe enabled

1 reel mammoth slot It does include a PCIe x16 slot, but rather than a second one, like Asus did with the E Gaming, it offers not one, but four PCIe enabled