checkbox indeterminate code example
Example: propriedades checkbox angular
<input type="checkbox" [checked]="opcao1" (change)="opcao1 = !opcao1" />
<input type="checkbox" [checked]="opcao2" (change)="opcao2 = !opcao2" />
<input type="checkbox" [checked]="opcao3" (change)="opcao3 = !opcao3" />