I switched the SDK for an existing project from 2.0.0 to 2.1.0. The vscode extension downloaded the new SDK (and updated toolchain). However, when I attempted to reconfigure and rebuild the project, there were multiple complaints about missing files. It was necessary for me to cd to ~/.pico-sdk/sdk/2.1.0 and run git submodule update --init manually to resolve them. After that, everything configured and built successfully.