title: ion-back-button is not showing up in toolbar in Ionic 5
body: <p>I'm trying to show a back button in the toolbar of one page.
  Below is excerpt of my code.</p>
  <pre><code>  &lt;ion-toolbar&gt;
      &lt;ion-buttons slot=&quot;start&quot;&gt;
        &lt;ion-back-button [text]=&quot;&quot; [icon]=&quot;arrow-back&quot;&gt; &lt;/ion-back-button&gt;
      &lt;/ion-buttons&gt;
      &lt;ion-title&gt;
        About
      &lt;/ion-title&gt;
    &lt;/ion-toolbar&gt;
  </code></pre>
  <p>If I set the  <code>defaultHref</code> attribute, it works but I will not have ability to use my custom back button with <em>text</em> and <em>icon</em>.</p>
  <pre><code>  &lt;ion-toolbar&gt;
      &lt;ion-buttons slot=&quot;start&quot;&gt;
        &lt;ion-back-button defaultHref=&quot;home&quot;&gt; &lt;/ion-back-button&gt;
      &lt;/ion-buttons&gt;
      &lt;ion-title&gt;
        About
      &lt;/ion-title&gt;
    &lt;/ion-toolbar&gt;
  </code></pre>
  <p>How do I make it work. Could anyone please help?</p>