So you're trying to upgrade to Flat Config, but ESLint config for Airbnb's TypeScript rules (`eslint-config-airbnb-typescript`) is not being upgraded automatically.

The issue might be that `eslint-config-airbnb-typescript` is a custom ESLint configuration that needs to be explicitly migrated to the new Flat Config format. Here are some steps you can follow to achieve this:

1. First, update your `eslintrc.json` file to the new Flat Config format. You can do this by running the command:
```bash
npx @eslint/eslint-config-generator --type flat
```
This will generate a new `eslintrc.json` file in the root of your project.

2. Next, you need to update the `extends` property in your new `eslintrc.json` file to include the Airbnb TypeScript configuration. You can do this by adding the following line:
```json
"extends": ["airbnb/typescript", "eslint-config-flat"],
```
This tells ESLint to use the Airbnb TypeScript configuration and the Flat Config format.

3. Finally, you need to update your `tsconfig.json` file to include the necessary configurations for Airbnb's TypeScript rules. You can do this by adding the following lines:
```json
"extends": ["airbnb/typescript"],
"rules": {
  "@typescript-eslint/no-unused-vars": "error",
  // Add other rules as needed
}
```
This tells TypeScript to use the Airbnb TypeScript configuration and includes specific rules for unused variables.

After completing these steps, you should be able to use the new Flat Config format with ESLint and TypeScript. If you encounter any issues or have further questions, feel free to ask!