I was wondering that, too. I couldn't find the actual model of the monitor anywhere on the page. But LG has several monitors in its UltraGear line that do 3440x1440 at 144Hz: https://www.lg.com/us/gaming-monitors Presumably he's got one of them?
In that case it's not so much the EDID that's wrong but something else in his setup that won't work with those capabilities, and either Windows and Apple just don't default to maxing out the refresh rate, or they do but are able to detect that it's the wrong cable. Or it's a graphics driver issue?
I wouldn't be surprised if MacOS and Windows simply default to 60Hz unless manually selected otherwise, just to reduce customer service tickets.
Debugging this issue on linux is maybe an exciting journey, debugging it over the phone with a end-user who only has one cable and one monitor is just a PITA.
In that case it's not so much the EDID that's wrong but something else in his setup that won't work with those capabilities, and either Windows and Apple just don't default to maxing out the refresh rate, or they do but are able to detect that it's the wrong cable. Or it's a graphics driver issue?