How to render a text with linebreak saved from a textarea form?
I tried putting the value in a '#markup' =&gt; $text render array, but it
  was the same. How can I render this new line?


Yes, you need to put the text in a render element, but for a formatted text field the correct element is processed_text:

'text' =&gt; [
  '#type' =&gt; 'processed_text',
  '#text' =&gt; $node-&gt;field_text-&gt;value,
  '#format' =&gt; $node-&gt;field_text-&gt;format,
],