An example context aware block that combines two fields to be used in Layout Builder

FullNameBlock.php

<?php

namespace Drupal\example\Plugin\Block;

use Drupal\Core\Block\BlockBase;
use Drupal\Component\Render\FormattableMarkup;

/**
 * Provides the full name of the author of the given node from context.
 *
 * @Block(
 *   id = "full_name",
 *   admin_label = @Translation("Full name block"),
 *   context = {
 *     "node" = @ContextDefinition("entity:node", required = FALSE)
 *   }
 * )
 */
class FullNameBlock extends BlockBase {

  /**
   * {@inheritdoc}
   */
  public function build() {

    /** @var \Drupal\node\NodeInterface $node */
    $node = $this->getContextValue('node');

    return [
      '#markup' => new FormattableMarkup('@firstname @lastname', [
        '@firstname' => $node->getOwner()->field_firstname->value,
        '@lastname' => $node->getOwner()->field_lastname->value,
      ]),
    ];

  }

}