I tried the following setup however it did not work.

% which npx
/usr/local/bin/npx

{
  "mcpServers": {
    "filesystem": {
      "command": "/usr/local/bin/npx",
      "args": [
        "-y",
        "@modelcontextprotocol/server-filesystem",
        "/Users/xxx/Desktop"
      ]
    }
  }
}

However, I tried the following setup and this worked. Perhaps this was a path issue.

% which node
/usr/local/bin/node

{
  "mcpServers": {
    "filesystem": {
      "command": "/usr/local/bin/node",
      "args": [
        "/usr/local/lib/node_modules/@modelcontextprotocol/server-filesystem/dist/index.js",
        "/Users/xxx/Desktop"
      ]
    }
  }
}