As I can see the spring boot's ElasticsearchRestClientAutoConfiguration might happen after ElasticsearchEvolutionAutoConfiguration.
I see that ElasticsearchEvolutionAutoConfiguration contains the code:
@AutoConfigureAfter(name = {
"org.springframework.boot.autoconfigure.elasticsearch.rest.RestClientAutoConfiguration" // since spring-boot 2.1
})
But I do not see the org.springframework.boot.autoconfigure.elasticsearch.rest.RestClientAutoConfiguration and I see org.springframework.boot.autoconfigure.elasticsearch.ElasticsearchRestClientAutoConfiguration in spring boot 2.4.3. May be it was replaced?
As a result the RestHighLevelClient is configured by elasticsearch-evolution and some configuration parameters like spring.elasticsearch.rest.username are not supported.
I suggest to add extra line into @AutoConfigureAfter.