Witcher 3 launched for the PS4, PC and Xbox One in 2015. It was a great success for CD Project Red and managed to sell through more than 10 million units worldwide.
While CD Project Red is currently working on Cyberpunk 2077, a French wholesaler has listed The Witcher 3 for Nintendo Switch. Normally, retailer listings with a credible track record are not wrong but in this case, it seems a bit far-fetched to expect this for the Nintendo Switch. What seems to be the more likely outcome is that CD Project Red ports Thronebreaker: Witcher Tales or Gwent to the Nintendo Switch.
If you want to take a look at the listing yourself, it can be found here. There are a lot of mistakes in the listing so it would be early to call this legitimate leak. It can always be an unintentional mistake where a game in the same franchise is labeled incorrectly.
In addition to The Witcher 3, CD Project Red released Gwent: The Witcher Card Game and more recently, Thronebreaker: The Witcher Tales. Both of these are good candidates for the Nintendo Switch hardware while the open world nature and demanding requirements of The Witcher 3 make it the least likely candidate to get ported to the Nintendo Switch, provided if this listing is even accurate in the first place.