How do I have a dropdown select list for an entity reference? For Drupal 8, the entity reference field displayed in form is a textfield with auto-complete feature for you to select the entity, is it possible to have it be dropdown select list instead? I have tried using views as the reference method to check the possible solution, but without luck, someone can help me with this?
Yes, you can. Drupal 8 does it out of the box as D7. The only difference is you can now choose the widget for any field in the Manage form display tab of a entity type.

E.g. Try changing the widget of the entity reference field - Tags - for article content type from /admin/structure/types/manage/article/form-display