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

I see various mobos with, for example, 'half-length' PCIe x16 slots But this is a contradiction in terms A PCIe x16 slot by definition is

List of Motherboards with 3 PCI-Express x16 Slots: GIGABYTE B650 Gaming X AX V2, MSI X670E Gaming Plus WiFi, ASUS ROG Strix Z790-E Gaming WiFi II,

pciex4 slot A x8 card will work in an x1 slot, but will be limited to x1 speeds A x8 card will also work fine in a x4 slot It will be limited to x4 speeds

pcie 30 in 40 slot A PCIe x8 card will fit in any PCIe x8 or PCIe x16 slot PCIe cards larger than the PCIe slot may fit in the smaller slot but only if it is open