To achieve the parallel processing of PostCSS files and load them as a separate CSS bundle in your Webpack setup with React, TypeScript, and CSS/LESS, you can follow these steps:

### 1. Install Necessary Dependencies
First, make sure you have the necessary PostCSS and Webpack loaders installed:

```bash
npm install postcss-loader postcss-preset-env css-loader style-loader mini-css-extract-plugin --save-dev
```

### 2. Configure PostCSS
Create a `postcss.config.js` file in the root of your project to configure PostCSS with popular plugins. Here’s an example configuration:

```javascript
module.exports = {
  plugins: [
    require('postcss-preset-env')({
      stage: 1,
      features: {
        'nesting-rules': true,
      },
    }),
    // Add more PostCSS plugins as needed
  ],
};
```

### 3. Webpack Configuration
Next, update your Webpack configuration to handle both your regular CSS/LESS files and the PostCSS files separately.

Here’s an example `webpack.config.js`:

```javascript
const path = require('path');
const MiniCssExtractPlugin = require('mini-css-extract-plugin');

module.exports = {
  entry: {
    main: './src/index.tsx',
    styles: './src/styles/main.postcss'  // Entry point for PostCSS
  },
  output: {
    filename: '[name].js',
    path: path.resolve(__dirname, 'dist'),
  },
  module: {
    rules: [
      // Rule for regular CSS/LESS
      {
        test: /\.(css|less)$/,
        use: [
          MiniCssExtractPlugin.loader,
          'css-loader',
          'less-loader',
        ],
      },
      // Rule for PostCSS files
      {
        test: /\.postcss$/,
        use: [
          MiniCssExtractPlugin.loader,
          'css-loader',
          'postcss-loader',
        ],
      },
      // Rule for TypeScript
      {
        test: /\.tsx?$/,
        use: 'ts-loader',
        exclude: /node_modules/,
      },
    ],
  },
  resolve: {
    extensions: ['.tsx', '.ts', '.js'],
  },
  plugins: [
    new MiniCssExtractPlugin({
      filename: '[name].css',  // This will generate separate CSS files for each entry point
    }),
  ],
};
```

### 4. Create PostCSS Files
Now, create a `.postcss` file in your source directory:

```css
/* src/styles/main.postcss */
:root {
  --main-color: #3498db;
}

body {
  font-family: 'Arial', sans-serif;
  color: var(--main-color);
}

/* More PostCSS code */
```

### 5. Import CSS/LESS and PostCSS in Your React Components
In your React components, you can import the regular CSS/LESS files as usual. The PostCSS files will be bundled separately and loaded via the entry point you defined.

Example:

```javascript
import React from 'react';
import './styles/app.less';  // Regular CSS/LESS

const App = () => {
  return <div>Hello, World!</div>;
};

export default App;
```

### 6. Build Your Project
Run your Webpack build to generate the separate CSS bundles:

```bash
npm run build
```

This setup will generate two CSS files in the `dist` directory:

- `main.css` for your standard CSS/LESS styles.
- `styles.css` for the PostCSS processed styles.

These will be loaded separately when you include them in your HTML or within your React application.

### 7. Include the Bundles in HTML (if necessary)
If you're manually including the CSS bundles in your HTML, it would look something like this:

```html
<link rel="stylesheet" href="dist/main.css">
<link rel="stylesheet" href="dist/styles.css">
```

This configuration ensures that your PostCSS files are processed separately with the desired plugins and are output as a separate CSS bundle.