Getting "inject() must be called from an injection context" after upgrading to Angular 11

After upgrading to Angular 11, I am not able to ng serve my web application anymore.

The problem appears to be related to my (generated) REST-client. Opening https://localhost:4200 will write the following into the console:

main.ts:12 Error: inject() must be called from an injection context
    at injectInjectorOnly (core.js:4901) [angular]
    at Module.ɵɵinject (core.js:4911) [angular]
    at Object.ApiModule_Factory [as factory] (meditation-rest-client.js:2885) [angular]
    at R3Injector.hydrate (core.js:11158) [angular]
    at R3Injector.get (core.js:10979) [angular]
    at :4200/vendor.js:82591:55 [angular]
    at Set.forEach (<anonymous>) [angular]
    at R3Injector._resolveInjectorDefTypes (core.js:11016) [angular]
    at new NgModuleRef$1 (core.js:25046) [angular]
    at NgModuleFactory$1.create (core.js:25100) [angular]
    at :4200/vendor.js:100468:45 [angular]
    at Object.onInvoke (core.js:28301) [angular]

The following is my tsconfig.json file:

/* To learn more about this file see: */
  "compileOnSave": false,
  "compilerOptions": {
    "baseUrl": "./",
    "outDir": "./dist/out-tsc",
    "sourceMap": true,
    "declaration": false,
    "downlevelIteration": true,
    "experimentalDecorators": true,
    "moduleResolution": "node",
    "importHelpers": true,
    "target": "es2015",
    "module": "es2020",
    "lib": [

This is how I define the dependency in package.json

    "chart.js": "^2.9.4",
    "core-js": "^3.8.2",
    "meditation-rest-client": "./generated/meditation-rest-client",
    "http-server": "^0.12.3",
    "http-status-codes": "^2.1.4",
    "moment": "^2.29.1",

And this here are those generated lines which are reffered to in the error message above:

// ...

ApiModule.ɵmod = ɵngcc0.ɵɵdefineNgModule({ type: ApiModule });
ApiModule.ɵinj = ɵngcc0.ɵɵdefineInjector({ factory: function ApiModule_Factory(t) { return new (t || ApiModule)(ɵngcc0.ɵɵinject(ApiModule, 12), ɵngcc0.ɵɵinject(ɵngcc1.HttpClient, 8)); }, providers: [], imports: [[]] });
ApiModule.ctorParameters = () => [
    { type: ApiModule, decorators: [{ type: Optional }, { type: SkipSelf }] },
    { type: HttpClient, decorators: [{ type: Optional }] }

// ...

This used to work in Angular 9 but it won’t under Angular 11.

Any idea how to fix this? I already tried setting "preserveSymlinks": true as suggested here and here.

Please let me know if you need more information.

Source: Angular Questions