Updating a game via NSP requires a matching update file. Because the Legacy Edition is discontinued, you will not find new feature updates for it. Nintendo Switch Edition - Minecraft Wiki
Development for this edition officially stopped after the World of Color Update .
Finding the "actual update" for Minecraft: Nintendo Switch Edition can be confusing because there are two distinct versions of the game on the platform. If you are using an for the original legacy version, here is everything you need to know about the final updates and how they differ from the modern Bedrock version. The Final Version: Minecraft Nintendo Switch Edition