Remove bottom border from <ion-item> in Ionic 6

<ion-item lines="none" class="NewAccount-input">
     <ion-input #nameuser class="ContactForm-input" type="text" placeholder="Nombre de Usuario *" formControlName="nombreusuario"></ion-input>
</ion-item>

Your code should work. You also can use CSS to archive this:

ion-item.no-border {
  --border-width: 0;
}

<ion-item class="no-border"></ion-item>