OpenSearch (1.x and 2.x) is the only supported ElasticSearch implementation (ES 6 is EOL since 10 months) that is libre/open source. The license change starting with ES 7.11 isn't considered libre/open source by Debian, Fedora and the OSI.

Having it officially tested and supported would have a lot of value for MediaWiki admins that want to keep a libre stack. (even though OpenSearch is developed by Amazon...)

As of now according to:
https://www.mediawiki.org/wiki/Extension:CirrusSearch

MediaWiki 1.39+ require Elasticsearch 7.10.2

A managed product like Amazon OpenSearch (formerly Amazon Elasticsearch) can work but may require additional configuration depending on its specifics. [...]

So OpenSearch 1.x (which is aimed to be a drop in replacement for ES 7.x) might work unless CirrusSearch does version checks.

For example, Amazon OpenSearch only listens for Elasticsearch API requests over HTTPS on port 443 (i.e. it does not expose the default Elasticsearch port 9200), so a TLS-enabled proxy (e.g. Nginx) can enable CirrusSearch to communicate with an Amazon OpenSearch cluster.

That shouldn't be the case with self hosted OpenSearch. I tried on a project to migrate from ES to OpenSearch and the official docker image listens to 9200 and I didn't have to set up a proxy.

So the request is to have OpenSearch (at least 1.x for now) tested and integrated in the QA process and hopefully not much is needed to claim official support for OpenSearch alongside ElasticSearch