The new way to register beans in a functional way is coming to Spring Framework 7:
spring-projects/spring-framework#18353 (comment)

We need to add a new validation:

• for every class that implements BeanRegistrar, there should be an @Import(..) for that class in some configuration
• quick fix should allow users to add this @Import to existing configuration classes, or create a new configuration class with that @Import
  • difficulty might be that a config class already has an @Import annotation, in which case the bean registrar type should be added to that @Import annotation for that config class

@Configuration
@Import(MyBeanRegistrar.class)
public class MyConfiguration {
}
public class MyBeanRegistrar implements BeanRegistrar {
...