And lets apply some common sense to your common sense, follow up on it a little. If a modifier is defined by the fact that it modifies the actions of other keys, then left and right modifer keys modify the action in exactly the same way and thus are the same modifier. Common sense indeed.
And if you want to reference windows, a platform kitty does not support, here you go: https://developer.apple.com/documentation/appkit/nseventmodi...
no left and right modifier state on macOS. And neither does X11/Wayland have them, though I dont have a link handy, so I will just leave you with a couple of links to the documentation for cross platform toolkits instead:
https://doc.qt.io/qt-6/qt.html#KeyboardModifier-enum https://www.glfw.org/docs/latest/group__mods.html
And in case the common sense didnt make it past your mental barriers, a terminal keyboard protocol has to work on all platforms not just windows. The good lord alone knows what windows does, probably synthesizes that state based on press and release events.