You can do this:
<ng-template ngFor let-user [ngForOf]="users$ | async" *ngIf="(users$ | async)?.length > 1 && (users$ | async)?.length < 5">
<div>{{ user | json }}</div>
</ng-template>
Keep in mind that when using a subscription from a http-request, this would trigger the request twice. So you should use some state-management pattern or library, to not make that happen.
Here is a stackblitz.