Override getReferenceableBundles() method

I think this is a dupe of ✨ Dynamic Entity Reference normalization support Active can you confirm?

Nope, it isn't related.
In 🐛 ResourceTypeRepository wrongly assumes that all entity reference fields have the setting "target_type" Fixed they have added the \Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItemInterface that has a static getReferenceableBundles() method.

\Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItem implements that method with using 'target_type' option.

Your class DynamicEntityReferenceItem inherits that method but it won't work for dynamic reference since it doesn't have a 'target_type' option.

The issue you've linked is another core issue related to dynamic entity reference support.

This one is about your module having to adapt to solution provided in #3057545

This is a duplicate of 🐛 Implement EntityReferenceItemInterface Needs work .