How to Use Spring Boot's 'spring.jackson.date-format' Property?
That property is only used for the java.util.Date serialization and not java.time.* classes.
You can have on demand (per field) format specified with @JsonFormat(pattern="dd.MM.yyyy")
or
Create a bean that implements the org.springframework.boot.autoconfigure.jackson.Jackson2ObjectMapperBuilderCustomizer interface and setup custom serializers on the ObjectMapper for java.time.* classes that use a more sensible format.