The "field_item:feeds_serialized" plugin does not exist.

This is a field type deleted almost three years ago. See https://git.drupalcode.org/project/feeds/commit/b73b5702f7280f7763669335... and #2728621: Adding modules that hook into the feed config is not working.

Since Drupal 8.7, Drupal no longer supports automatic entity updates, so that's probably why you see this error since that version: https://www.drupal.org/node/3034742.

Hopefully one of the methods described on that page would help you further. Perhaps "Updating an existing field storage definition"?

function example_update_8701() {
  $entity_definition_update_manager = \Drupal::entityDefinitionUpdateManager();
  $field_storage_definition = $entity_definition_update_manager->getFieldStorageDefinition('hostname', 'comment');
  $field_storage_definition->setDefaultValueCallback(Comment::class . '::getDefaultHostname');
  $entity_definition_update_manager->updateFieldStorageDefinition($field_storage_definition);
}

Instead of changing the default value as above, the field type should be changed for the field 'config' on the feed entity type, so I assume you need to start with the following:

$entity_definition_update_manager = \Drupal::entityDefinitionUpdateManager();
$field_storage_definition = $entity_definition_update_manager->getFieldStorageDefinition('config', 'feeds_feed');

When we have the site on 8.6 that does support entup, it comes back saying there’s no entity configuration to update. Should it not register this need when on the core branch that supports it?

I don't know. Maybe entup doesn't support field type changes.

I am running into the same issue can you elaborate on what

$field_storage_definition->setDefaultValueCallback(Comment::class . '::getDefaultHostname'); 

should be in the example for feeds_feed?
note that the structure of $field_storage_definition from

$field_storage_definition = $entity_definition_update_manager->getFieldStorageDefinition('config', 'feeds_feed');

is :

Drupal\Core\Field\BaseFieldDefinition Object
(
    [type:protected] => feeds_serialized // I believe this should be 'map' instead of 'feeds_serialized' . It is probably possible to update this. 
    [propertyDefinitions:protected] => 
    [schema:protected] => Array
        (
            [columns] => Array
                (
                    [value] => Array
                        (
                            [type] => blob
                            [size] => big
                            [serialize] => 1
                        )

                )

            [unique keys] => Array
                (
                )

            [indexes] => Array
                (
                )

            [foreign keys] => Array
                (
                )

        )

    [indexes:protected] => Array
        (
        )

    [itemDefinition:protected] => Drupal\Core\Field\TypedData\FieldItemDataDefinition Object
        (
            [fieldDefinition:protected] => Drupal\Core\Field\BaseFieldDefinition Object
 *RECURSION*
            [definition:protected] => Array
                (
                    [type] => field_item:feeds_serialized
                    [settings] => Array
                        (
                        )

                )

            [typedDataManager:protected] => 
        )

    [definition:protected] => Array
        (
            [label] => Drupal\Core\StringTranslation\TranslatableMarkup Object
                (
                    [translatedMarkup:protected] => 
                    [options:protected] => Array
                        (
                        )

                    [stringTranslation:protected] => 
                    [string:protected] => Config
                    [arguments:protected] => Array
                        (
                        )

                )

            [description] => Drupal\Core\StringTranslation\TranslatableMarkup Object
                (
                    [translatedMarkup:protected] => 
                    [options:protected] => Array
                        (
                        )

                    [stringTranslation:protected] => 
                    [string:protected] => The config of the feed.
                    [arguments:protected] => Array
                        (
                        )

                )

            [provider] => feeds
            [field_name] => config
            [entity_type] => feeds_feed
            [bundle] => 
        )

    [typedDataManager:protected] => 
)

This exist in the key_value table in the database.

so to fix this issue, the best way to do it is to uninstall and reinstall the feeds module. However this is sometimes difficult without deleting all feeds entities. I was able to mock the process by doing to following in a hook update:

  // Read the configuration.
  $module_data = \Drupal::config('core.extension')->get('module');
  // Unset the modules you do not need.
  unset($module_data['feeds']);

  
  \Drupal::configFactory()
    ->getEditable('core.extension')
    ->set('module', $module_data)
    ->save();
  // Delete a configuration object in order to reinstall
  $config = Drupal::configFactory()
    ->getEditable('system.action.feeds_feed_delete_action');
  if ($config) {
    $config->delete();
  }
  // Reinstall the schema
  \Drupal::service('module_installer')->install(['feeds']);

this worked without any obvious repercussions.
@MegaChriz do you have any thoughts on this?

@awm
Your code seems like a hack, but if it works, then that's great! Looks weird that specifically the action plugin instance needs to be deleted. But feed types, feeds and feeds_item fields can thus all stay in place without the need to deleting these?

So 'feeds_serialized' cannot be changed to 'map' with the entity definition update manager?

@MegaChriz uninstalling the module and re-installing is what I determined was the best way. However, upon uninstalling the module the action remained, which I reckon is a feeds bug. This prevented me from re-installing the module and thus I needed to delete it.

Do you agree uninstalling and re-installing the cleanest way to address such a problem?

It is possible to update but I have not tried, can you post sample code how how to update it using the manager?

Finally I opted for re-installing the module because I was not sure if that's the only issue that will be encountered.

@awm
Finding out how to update is what I hope you or @kferencz91 would find out ;). I don't know the answer, at least not without diving into it myself.

If the action remains upon uninstalling, then that sounds like a bug. Perhaps you want to create a new issue for that? Perhaps you also want to write a test for reinstalling Feeds? It can be added to the existing \Drupal\Tests\feeds\Functional\FeedsUninstallTest.

I am having this same error with feeds. I am trying to delete the feeds in order to uninstall/re-install the module but it keeps erroring out when I try to delete the feeds. This is the first part of a mile-long error log entry: Error: Maximum function nesting level of '256' reached, aborting! in Drupal\Core\Entity\EntityType->isSubclassOf() (line 450 of /app/web/core/lib/Drupal/Core/Entity/EntityType.php).