Pre fill multiple paragraphs while adding node
You can't reuse existing paragraphs, you have to create new paragraphs for each node:

$paragraph1 = Paragraph::create([
  'title' =&gt; 'Paragraph 1',
  'type' =&gt; 'paragraph_type1',
]);
$paragraph1-&gt;save();

$paragraph2 = Paragraph::create([
  'title' =&gt; 'Paragraph 2',
  'type' =&gt; 'paragraph_type2',
]);
$paragraph2-&gt;save();

$node = Node::create([
  'title' =&gt; 'Node with two paragraphs',
  'type' =&gt; 'article',
  'field_paragraph' =&gt; [$paragraph1, $paragraph2],
  ]);
$node-&gt;save();


You could place this code in a custom controller:

  public function addCustomContentType() {
    $node = $this-&gt;entityTypeManager()-&gt;getStorage('node')-&gt;create([
      'type' =&gt; 'custom_content_type',
    ]);

    // create paragraphs, don't save them yet, in case the node is not submitted

    $paragraph1 = $this-&gt;entityTypeManager()-&gt;getStorage('paragraph')-&gt;create([
      'title' =&gt; 'Paragraph 1',
      'type' =&gt; 'paragraph_type1',
       // more field data
    ]);

    $paragraph2 = $this-&gt;entityTypeManager()-&gt;getStorage('paragraph')-&gt;create([
      'title' =&gt; 'Paragraph 2',
      'type' =&gt; 'paragraph_type2',
      // more field data
    ]);

    // prefill the paragraph field in the node with the paragraphs
    $node-&gt;field_paragraph = [$paragraph1, $paragraph2];

    $form = $this-&gt;entityFormBuilder()-&gt;getForm($node);

    return $form;