Roblox appears to encourage detection of the user’s control scheme rather than their platform. There was a feature request some time ago that asked for a way to directly access the user’s platform, and one of the concerns was that developers might make certain controls accessible for, say, Xbox, but then not PS4 by accident, instead of the current system where you can just figure out that the user is on a controller, do whatever you want with that, and people can plug in controllers to their PCs to play without hiccups.
I don’t think it’s really necessary, and apparently neither do Roblox, when they already provide a way to use user input based on control scheme rather than platform. Bringing up the PC + controller example mentioned previously, what would the platform be? If it said “Windows”, then developers will just assume that player’s are using a keyboard and a mouse, making it difficult to use a controller on PC if that’s really what someone wants to do.