Drupal 8: Create and update custom block in hook_update()

my_module.install.php

<?php

/**
 * Keep yours custom block in code!
 *
 * This approach let you avoid this error:
 * "This block is broken or missing. You may be missing content or you might need to enable the original module."
 */

/**
 * Create new custom block.
 */
function my_module_update_8001(){
  $block_body = <<<EOF
<div class="my-awesome-block">
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Aliquam enim urna, tempor ut ultrices non, blandit quis nulla. Nulla facilisi.
</div>
EOF;

  $blocks = [
    'block_content' => [
      'a1e23473-ecac-4ad1-8308-80edc0114141' => [
        'info' => 'User links',
        'type' => 'basic',
        'body' => [
          'value' => $block_body,
          'format' => 'full_html',
        ],
      ],
    ],
  ];

  foreach ($blocks as $block_type => $items) {
    $storage = \Drupal::entityTypeManager()->getStorage($block_type);
    foreach ($items as $uuid => $item) {
      if (\Drupal::service('entity.repository')->loadEntityByUuid($block_type, $uuid) == FALSE) {
        $entity = $storage->create($item + ['uuid' => $uuid]);
        $entity->save();
      }
    }
  }
}


/**
 * Update custom block.
 */
function my_module_update_8002(){
  $block_type = 'block_content';
  $block_uuid = 'b399d911-f137-4d80-9f15-21f4ca230ba7';
  $block_body = <<<EOF
<div class="my-awesome-block">
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Aliquam enim urna, tempor ut ultrices non, blandit quis nulla. Nulla facilisi.
</div>
EOF;

  if ($block = \Drupal::service('entity.repository')->loadEntityByUuid($block_type, $block_uuid)) {
    $block->set('body', [
      'value' => $block_body,
      'format' => 'full_html',
    ]);
    $block->save();
  }
}