You don't have any annotations on Hostel. Hostel.builder() is really a masquerading Hotel.builder().

So the assignment would have to be

final Hotel<?> build = Hostel.builder().build();

Or more accurately (making static methods subject to inheritance was IMO a mistake)

final Hotel<?> build = Hotel.builder().build(); 

You probably want to add some Lombok annotations to the child class.

Customizing @SuperBuilder only works in more recent lombok version; you should always use the most recent one, which is v1.18.22 at the time of the writing of this answer.

With that version, customizing a @SuperBuilder constructor is possible. However, you are using code as a basis for your constructor that has been delomboked with v1.18.8. That does not work any more with current lombok versions. lombok v1.18.10 introduced that the actual field value for @Default fields are stored in the builder in fields like fieldName$value, not simply fieldName.

Thus, your customized constructor has to look as follows:

protected ApplicationUser(final ApplicationUserBuilder<?, ?> b) {
    super(b);
    this.application = b.application;
    if (b.groups$set) this.setGroups(b.groups$value);
    else this.setGroups(ApplicationUser.$default$groups());
}

You shouldn't mix lombok @Builder with static inner Builder class. If it is possible to get rid of Builder class, the next code should work.

RequestMessage:

@Getter
@ToString
@EqualsAndHashCode(callSuper = true)
@SuperBuilder(toBuilder = true)
@AllArgsConstructor(access = AccessLevel.PRIVATE)
public class RequestMessage extends MyDTO {
    private final String name;

    @Override
    public String emitSerializedPayload() throws JsonProcessingException {
    return null;
    }
    public RequestMessage(String myAccountId, String name) {
        super(myAccountId);
        this.name = name;
}
}

MyDTO:

@Data
@SuperBuilder(toBuilder = true)
public abstract class MyDTO implements Serializable {
    @JsonIgnore private final ObjectMapper objectMapper = new ObjectMapper();
    protected String myAccountId;

    protected MyDTO() {}

    public MyDTO(String myAccountId) {
       this.myAccountId = myAccountId;
    }

    public static int hashCode(Object... objects) {
        return Arrays.deepHashCode(objects);
    }

    public static boolean equal(Object o1, Object o2) {
        // implementation of equals method
        return false;
    }
    public abstract String emitSerializedPayload() throws JsonProcessingException;
}

Test:

@Test
void name() {
    String myName = "myName";
    String myAccountId = "myAccountId";
    var request = RequestMessage.builder().name(myName).myAccountId(myAccountId).build();
    System.out.println("request = " + request);
    RequestMessage requestMessage = new RequestMessage(myAccountId, myName);
}