How to use DataDefinition::create('list')?
ItemList is a generic base class. List is used here in the context of multivalued field items. Because Drupal has no separate class for single value fields (they are multivalued fields restricted to one value), this generic list data type is used in all Drupal fields.

When you look at the list of field types

https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Field%21Annotation%21FieldType.php/class/annotations/FieldType/8.4.x

you'll find ListStringItem, where List is used in the context you are probably looking for and you can use this as an example for this kind of field types implementing OptionsProviderInterface.