If the game asks for a “Software Update” but you already installed the NSP, you may need to disable “System Update Check” in Tinfoil’s settings or update your Switch’s firmware to the latest compatible version (typically 17.0.0+ for 2024 releases).
While the Switch receives all free seasonal updates , the paid "Mechanized" DLC was not released for this platform. Core Gameplay Features SteamWorld Build Switch NSP -Update- -eShop-