Mixed DML: Setup and Non-Setup Objects in the Same Transaction

// Use @future or Queueable to separate the transactions
public class OnboardingService {
    public static void createUserAndAccount(
        String lastName, String email
    ) {
        User u = new User(
            LastName = lastName, Email = email
            // ... required fields
        );
        insert u;
        // Non-setup DML in a separate context
        createAccountAsync(u.Id, lastName);
    }

    @future
    private static void createAccountAsync(
        Id userId, String name
    ) {
        Account a = new Account(
            Name = name, OwnerId = userId
        );
        insert a; // Different transaction. No conflict.
    }
}