Not sure is this any help? https://steamcommunity.com/groups/SteamClientBeta/announcements/detail/834683256454278286
I think it actually just works with controllers that say they are 360 controllers. I have a 'generic gamepad' that works and the Xbox One controller almost certainly works although I haven't tested it. Steam might be able to make your Switch/PS4 controller work but whether TS works with it is not something I know of. DS4Windows certainly works, however.