In rdf_sync.module, the hook_entity_bundle_field_info() implementation incorrectly type-hints both parameters as strings:
function rdf_sync_entity_bundle_field_info(string $entity_type, string $bundle): array {
According to the official Drupal API documentation, this hook may be invoked with $bundle = NULL when Drupal core or contrib modules (such as OG, TMGMT, or EntityFieldManager) attempt to retrieve field definitions for all bundles of a given entity type.
Strictly type-hinting $bundle as string violates Drupal's expected function signature and causes TypeError exceptions in PHP 8+ and Drupal 10/11 environments.
See https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Entity%21...
Relax the type hint to allow nullable $bundle:
function rdf_sync_entity_bundle_field_info(string $entity_type, ?string $bundle): array {
Active
1.0
Code
What I read in the link that you've mentioned (this one: https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Entity%21...) is that this hook provides field definitions for a specific bundle within an entity type. And the parameter's documentation is string $bundle: The bundle., not leaving the option for it to be NULL.