Can anyone clarify this? Thxs 
OpenSearch is officially supported and will receive upgrades as time goes.
ElasticSearch works, but is not supported nor recommended, as they switched from Apache to SSPL.
ElasticSearch’s latest apache version is 7.10.2 which is the one you can run on moqui 4 (and v3 also). This version by now is end-of-life with many vulnerabilities