StackBlitz SDK doesn't support Environment Variables as it's a StackBlitz Teams feature. Moreover, this extension will export everything that isn't node_modules, including secrets such as .env files.
FAQ
This extension doesn't work when I use Visual Studio Code inside WSL
There are 2 ways to solve this problem:
Install a web browser on the WSL environment and use it as the default handler for .html files
Use wslview to allow WSL to access host's browser.