The French website Nintendo Actu initially discovered how to make Joy-Cons operate on PCs back in 2017. Since then, they have been usable in many PC games unofficially. However, that was a constrained solution, as single-player games could only use either of the two controllers at once. Meanwhile, the official Steam support is significantly more thorough. You can enable them to be used “both singly as a mini-gamepad and coupled into pairs,” as well as reportedly having remappable buttons, per user comments. You must be enrolled in the Steam client beta in order to use the Joy-Con support, which is part of the most recent Steam beta version. To accomplish this, go to your Steam settings and search under the Account menu for “Beta participation.” You can proceed by clicking the “Change” button, choosing “Steam Beta Update,” and restarting the application.