The patch notes don't detail each and every controller that is supported, so The Verge reached out for clarification. Valve spokesperson Kaci Aitchison Boyle confirmed that the Switch-specific NES, SNES, Sega Genesis and Nintendo 64 controllers are all compatible with Steam.
https://www.techspot.com/news/95468-steam-adds-support-nintendo-switch-online-classic-controllers.html?utm_source=dlvr.it&utm_medium=blogger
https://www.techspot.com/news/95468-steam-adds-support-nintendo-switch-online-classic-controllers.html?utm_source=dlvr.it&utm_medium=blogger