The error is surprisingly accurate as the *ngIf directive expects true or false and uses the resulting expression to determine whether or not to render the HTML element in the DOM.
EXCEPTION: Invalid argument 'true' for pipe 'AsyncPipe' in [!user$.anonymouse | async in SettingsPage@27:22]
The expression you have is user$.anonymouse which evaluates as truthy, but unfortunately you cannot use the async pipe with this directive. The async pipe "transforms" (also known as "pipes") the input exposing the resulting output within the scope of the *ngFor directive for example.
The pipe expects one of three possible types, defined below ( detailed about AsyncPipe ):
transform(obj: Observable<any>| Promise<any>| EventEmitter<any>)
Is there any way how to solve this?
Yes, you can either use it as it was designed. For example in an *ngFor directive:

<ion-item *ngFor="(user$ | async)?.anonymouse">
     <ion-label>Login</ion-label>
</ion-item>

Or you could remove the piping altogether as it's not needed for the *ngIf directive:

<ion-item *ngIf="user$.anonymouse">
     <ion-label>Login</ion-label>
</ion-item>

As stated in the comments by @Sean, your *ngIf statement should be based on the resulted object property anonymouse of the user$ object that is returned. As such:

<ion-item *ngIf="(user$ | async)?.anonymouse">
     <ion-label>Login</ion-label>
</ion-item>

This worked for me and here is an example of how to use the results from the pipe below:

Component

message$: Observable<{message: string}>;

  private messages = [
    {message: 'You are my hero!'},
    {message: 'You are the best hero!'},
    {message: 'Will you be my hero?'}
  ];

  constructor() { this.resend(); }

  resend() {
    this.message$ = Observable.interval(500)
      .map(i => this.messages[i])
      .take(this.messages.length);
  }

View

<h2>Async Hero Message and AsyncPipe</h2>
<p>Message: {{ (message$ | async)?.message }}</p>
<button (click)="resend()">Resend</button>`

A working example can be found here .

<!-- This is needed to wait for async pipe to resolve -->
<div *ngIf="user$ | async as user"> 

   <!-- Only on resolve of async pipe -->
   <ion-item *ngIf="user.whateverPropertyYouWantToCheck">
        <ion-label>Login</ion-label>
    </ion-item>
</div>

请注意，我从user$切换到了user，如果愿意，您可以使用相同的变量名，但这更清楚地表明该值不再是异步管道。

如果你的用户是匿名的，那么你就可以使用这个方法。

<ion-item *ngIf="user$.anonymouse | async">