// Get the block
$block = DrupalblockEntityBlock::load('hightlight');

// Get the block content
$uuid = $block->getPlugin()->getDerivativeId();
$block_content = Drupal::service('entity.repository')->loadEntityByUuid('block_content', $uuid);

// Get the field value
$field = $block_content->get('field_link')->getValue()[0];

$value = $block_content->get('field_link')->getValue()[0];

$value = $block_content->get('field_link')->first()->getUrl()->toString();