routing for dynamic block for custom entity

For a custom entity I have created several dynamic blocks. But the blocks are not displayed. They are placed in admin/structure/block. Below is an example of block 1.

myentity.routing.yml:

myentity.blocks:
  path: '/collection/{myentity}'
  defaults:
    _title: 'Stuff collection'
  requirements:
    _permission: 'access content'
    myentity: \d+
  options:
    parameters:
      myentity:
        type: entity:myentity
        bundle:
            - a

Part of src/Plugin/Block:

namespace DrupalCorePluginBlock;

use DrupalCoreBlockBase;

/**
 * Provides a 'Collection' block.
 *
 * @Block(
 *   id = "collection_block 1",
 *   admin_label = @Translation("Collection: Stuff"),
 *   category = @Translation("My Collection"),
 *   context_definitions = {
 *     "myentity" = @ContextDefinition("entity:myentity", label = @Translation("Myentity ID"))
 *   }
 * )
 */
class MyentityBlock1 extends BlockBase {

  /**
   * {@inheritdoc}
   */
  public function build() {
    $myentity = $this->getContextValue('myentity');
    return [...];
}

If I replace myentity with node, it works, but for a custom entity I probably need to define something more. But what?

You can follow Providing global context variables. You have to create a new service to provide a context variable for your custom entity. You can use some entity node, user, taxonomy_term... because them already define.

https://git.drupalcode.org/project/drupal/-/blob/9.3.x/core/modules/taxonomy/taxonomy.services.yml#L7

  taxonomy_term.taxonomy_term_route_context:
      class: Drupal\taxonomy\ContextProvider\TermRouteContext
      arguments: ['@current_route_match']
      tags:
        - { name: 'context_provider' }

https://git.drupalcode.org/project/drupal/-/blob/9.3.x/core/modules/taxonomy/src/ContextProvider/TermRouteContext.php#L48

 /**
   * {@inheritdoc}
   */
  public function getRuntimeContexts(array $unqualified_context_ids) {
    $result = [];
    $context_definition = EntityContextDefinition::create('taxonomy_term')->setRequired(FALSE);
    $value = NULL;
    if ($route_object = $this->routeMatch->getRouteObject()) {
      $route_parameters = $route_object->getOption('parameters');

      if (isset($route_parameters['taxonomy_term']) && $term = $this->routeMatch->getParameter('taxonomy_term')) {
        $value = $term;
      }
      elseif ($this->routeMatch->getRouteName() == 'entity.taxonomy_term.add_form') {
        $vocabulary = $this->routeMatch->getParameter('taxonomy_vocabulary');
        $value = Term::create(['vid' => $vocabulary->id()]);
      }
    }

    $cacheability = new CacheableMetadata();
    $cacheability->setCacheContexts(['route']);

    $context = new Context($context_definition, $value);
    $context->addCacheableDependency($cacheability);
    $result['taxonomy_term'] = $context;

    return $result;
  }