multi-check-field-2.ts

private subscriptions = new Subscription();
private selectedValues: any[] = [];

ngAfterContentInit(): void {
  this.options.forEach(option => {
    this.subscriptions.add(
      option.valueChanges$.subscribe(
        (optionChecked) => {
          if (optionChecked) {
            this.add(option.value);
          } else {
            this.remove(option.value);
          }
        }
      )
    );
  });
}

private add(value: any): void {
  this.selectedValues.push(value);
}

private remove(value: any): void {
  const idx = this.selectedValues.findIndex(v => v === value);
  if (idx >= 0) {
    this.selectedValues.splice(idx, 1);
  }
}