In this point of 3.4 Release notes mention that:
Support for defining dynamic properties by injecting a DynamicPropertyRegistry has been deprecated and attempting to do so will now fail by default.
But it still seems to work and the release documentation still mentions DynamicPropertyRegistry as a mechanism for dynamic properties with test containers.
Comment From: wilkinsona
It's support for injection into a @Bean method that has been deprecated. In other words, instead of the approach described in https://docs.spring.io/spring-boot/3.3/reference/features/dev-services.html#features.dev-services.testcontainers.at-development-time.dynamic-properties, you should now use the approach described in https://docs.spring.io/spring-boot/reference/features/dev-services.html#features.dev-services.testcontainers.at-development-time.dynamic-properties.
@DynamicPropertySource methods, a Spring Framework feature, are unaffected. I've updated the release notes to hopefully make it clear that it's injection into @Bean methods that's affected by the deprecation.