Istanbul code coverage using Cypress in an Angular project can't find any files except main.ts

Question

I've got an Angular project, while using Cypress as the testing framework. Now I want to get the code coverage using nyc from Istanbul.

I've tried to make a minimal setup of the basic stuff right here: https://github.com/MichaelKoscheck/AngularCypressIstanbul

If I try to run yarn nyc yarn test now, the test file in cypress/e2e gets executed. But the sample spec I defined there tests a simple add method in the app.component.ts file. However the code coverage summary only includes the main.ts file.

What do I need to do so the app.component.ts gets included in the code coverage report?

I think the problem might be somewhere in the tsconfig.json, but I can't seem to find the solution. Or is this not working in general? If yes, what would I need to do to get to my desired outcome where the app.component.ts gets included into the code coverage report?

My .nycrc file:

{
  "all": true,
  "per-file": false,
  "check-coverage": true,
  "lines": 70,
  "skip-full": false,
  "extension": [".ts"],
  "include": "src/**/*.ts",
  "reporter": ["html", "text", "lcov", "cobertura"]
}

My tsconfig.json:

{
  "compileOnSave": false,
  "compilerOptions": {
    "baseUrl": "./",
    "outDir": "./dist/out-tsc",
    "forceConsistentCasingInFileNames": true,
    "strict": true,
    "noImplicitOverride": true,
    "noPropertyAccessFromIndexSignature": true,
    "noImplicitReturns": true,
    "noFallthroughCasesInSwitch": true,
    "declaration": false,
    "downlevelIteration": true,
    "experimentalDecorators": true,
    "moduleResolution": "node",
    "importHelpers": true,
    "target": "ES2022",
    "module": "ES2022",
    "useDefineForClassFields": false,
    "lib": [
      "ES2022",
      "dom"
    ]
  },
  "angularCompilerOptions": {
    "enableI18nLegacyMessageIdFormat": false,
    "strictInjectionParameters": true,
    "strictInputAccessModifiers": true,
    "strictTemplates": true
  }
}