Question - PCIE x8 into a PCIE x4

What is the point of even buying a video card that uses PCIe if people have motherboards that only have PCIe slots?

2 slot would the ADT-Link R43SG setup run at 32Gbps or 64Gbps? I have heard that high quality gen 3 cables could transfer at gen 4 speeds but

pcie slot gpu Contents · 1 Default Speed · 2 High Speed · 3 Ultra High Speed UHS-I; UHS-II; UHS-III · 4 SD Express microSD

pcie 40 in pcie 30 slot Historically, updates to PCIe doubled transfer rates and used multiples of 8 since generation With PCIe , bandwidth capacity is 64