After adding [(ngModel)] to a radio button group, the default [checked] no longer works

I think, you don’t need this [checked]="choice === defaultChoice". Try this :

<input type="radio"
       id="{{ groupName + choice }}"
       name="{{groupName}}"
       [value]="choice"
       [(ngModel)]="defaultChoice"
       (ngModelChange)="choose($event)" />

When [value] = [(ngModel)] the radio is selected.