VertX classes aren't being auto-configured in Spring Boot 3 applications due to spring.factories no longer being supported.
From the Spring Boot 3 Migration Guide:
Spring Boot 2.7 introduced a new META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports file for registering auto-configurations, while maintaining backwards compatibility with registration in spring.factories. With this release, support for registering auto-configurations in spring.factories has been removed in favor of the imports file.