Ion-select-option Customizing Individual Options does not work

I try to embed custom styles to ion-select-option as described here:
I take interface type ‘popover’.
If I use the code snippet (copy from your documentation):

// Pass a custom class to each select interface for styling
const select = document.querySelector('.custom-options');
select.interfaceOptions = {
  cssClass: 'my-custom-interface'

following error is shown:

TS2339: Property ‘interfaceOptions’ does not exists on type ‘Element’

I also tried setting PopoverOptions via using @ViewChild-Decorator for access IonSelect component. But PopoverOptions needs a component from type ‘ComponentRef’, and I doesn’t know, where I can get this.

My environment:

Ionic CLI : 6.19.0
Ionic Framework : @ionic/angular 6.1.2
@angular-devkit/build-angular : 12.2.15
@angular-devkit/schematics : 12.2.15
@angular/cli : 12.2.15
@ionic/angular-toolkit : 6.1.0