entity_reference autocomplete: Allow multiple target_types
entity_reference fields do not support multiple target types, never have, also not in Drupal 7 :) So you can't have an autocomplete for that as it couldn't be stored then.

However, you can use https://www.drupal.org/project/dynamic_entity_reference, which stores entity type and ID in a field and the default widget it provides is a combination of select and auto-complete field to select the type and the specific entity.