how do i hide a category when there are no items in it?

Try to use a ng-container with a *ngIf:

<div
 *ngFor="let cat of category| menuFiltered: (selected === -1 ? -1 : category[selected].id)" class="products">
  <ng-container *ngIf="plus | pluFiltered: men.id | pluSearch: searchModel as plusArray">
    <h2 *ngIf="plusArray.length > 0">{{ category.desc }}</h2>
     <div *ngFor="let plu of plusArray" class="row mb-3 product">
       ...
     </div>
  </ng-container>
</div>