Issue on upgrade 8708

I'm trying to update a Drupal website that was not maintained for a long time...

I've used `composer varbase-refactor-composer composer.new.json docroot` and the `composer update` but I get an error 500 while updating the database through the update.php script.

Here is the error I get :

Drupal\Core\Entity\Exception\FieldStorageDefinitionUpdateForbiddenException : The SQL storage cannot change the schema for an existing field (id in block_content entity) with data. dans Drupal\Core\Entity\Sql\SqlContentEntityStorageSchema->updateSharedTableSchema() (ligne 1887 de /var/www/vhosts/numerique-culturel.fr/dev.numerique-culturel.fr/20201209/docroot/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php).

How can I solve this ?

Thanks :-)