This is just talking about games approved through Valve's verification process. There are a lot of games that work that are "unverified", not to mention the entire history of gaming available through emulation.
According to this website, there are about 11k switch games. There are some duplicates on that list though, games which have multiple "editions" will have an entry under each version. For example, Xenoblade Chronicles DE is listed 4 times to cover different regional collectors editions.