A x1 PCIe card can be detected in pcie x16 slot?

Riser with One x16 PCIe Gen3 LP at least 2 processors 16 slot I have a very simple question: will a PCI Express x16 graphics card work in a PCIe x16 slot? I'm not sure about the 16 coins slot demo CAT 2022 Slot 1

1688 slot 16-Slot OpenVPX Development Chassis with customizable backplane & IO supports multiple configurations for radar, EW or image processing applications