Unchecking a boolean field on form render
You can use hook_ENTITY_TYPE_prepare_form() to change entity values before the entity form is built:

/**
 * Implements hook_ENTITY_TYPE_prepare_form() for Nodes.
 */
function mymodule_node_prepare_form(\Drupal\node\NodeInterface $node, $operation, \Drupal\Core\Form\FormStateInterface $form_state) {
  if ($node-&gt;getType() != 'my_content_type') {
    return;
  }
  if ($operation == 'edit') {
    $node-&gt;field_my_boolean_field-&gt;value = 0;
  }
}


This changes the value of the field for this node, but only temporary as long as the user doesn't submit the form.