How do I completely delete Cloud Datastore from a project?

This is the response I got from Google Cloud Support today (February 16th, 2021):

Generally, we do recommend to create a new project and enable Firestore therein. Nonetheless I may submit a request to delete your existing database which may allow you to change the database to the desired mode. However, please keep in mind that I’m unable to guarantee it’s approval.

Unfortunately, there is no way to purge the previous existence of a Cloud Datastore database to try either Cloud Firestore in native or Datastore mode. You'll have to use a new project to try Cloud Firestore in either native or Datastore mode.