They are capped at 60Hz at the resolution stated because the actual limiting value is the available bandwidth, and they are choosing to report the bandwidth in terms of "maximum 60Hz resolution".

If the limit is 6K at 60Hz, you'll be able to run 4K at >60Hz. My M1 MacBook Pro runs a 1440p monitor at 165Hz just fine over Thunderbolt 3.

The real function of interest was GetRawInputDevices (https://source.chromium.org/chromium/chromium/src/+/master:d...), not either of its two call sites. ;-)