How to enforce unique field with MongoDB in Spring

I have a pojo with two fields that need to be unique, the id and the email. So I added the @Indexed(unique = true) annotation to the necessary fields like so

public class User {
    @Id
    @Indexed(unique = true)
    private String id;
    @Indexed(unique = true)
    private String email;
    private int money;

I then tested it out and it was not enforced. So I googled about and I found a previous answer here - Spring Data: Unique field in MongoDB document and subsequently deleted the collection, added spring.data.mongodb.auto-index-creation=true to my application.properties file and tried again.

However, the unique field still isn't enforced! I see there is another answer using ensureIndex() but it also has a great comment that was never answered- Why do we need to use the annotation if all the work is done on mongoTemplate?

So since the question is old enough that apparently the only working answer is depreciated (the new way is using createIndex()), I thought it was time for a new version. Is it possible to require a column in a mongo collection to be unique from Spring Boot?