@MoInMaRvZ answered this here

We can simply add the code directly in the app.module.ts file. Like this:

 providers: 
    [
        provideHttpClient(withInterceptorsFromDi()),
        provideAnimationsAsync(),
        providePrimeNG({
        theme: {
        preset: Lara,
        options: {
        darkModeSelector: '.darkmode',
        },
        },
        }),
    ]