SDC is loading Post CSS files, not just compiled CSS files

This is a good suggestion.

But if you want to disallow the component using the postcss files add them in a subfolder inside the component and manage the compiling accordingly. Example:

/my-component/
- my-component.css
- my-component.twig
- my-component.yml
/pcss
- my-postcss-component.css

@TheodorosPloumis if you do that, the CSS file will be generated inside your /pscss folder (see core/scripts/css/postcss-build.js) and it will not be loaded by SDC, so in that case core assets compilation will need to be adjusted specifically for SDC. In any case, I think it's still a mistake that it loads anything that ends with .css as if it was a stylesheet, and it will probably prevent future problems to adjust this module for taking in account these cases.