[jakobson14]

inside the TB link there's no such thing as "3.0" or "x4"

hector goes over this as well, but basically you've replaced all the lower (physical) layers of PCIe's networking stack. intel like to pretend that thunderbolt and USB4 just tunnel actual PCIe links unchanged (as if they're emulating everything down the PCIe lanes and PHYs), but they don't. PCIe over thunderbolt can run at whatever speed you please, limited only by the throughput of TB and the overhead of the remaining layers of the PCIe stack.