We use OpenSearch on a number of our projects, as an open source alternative to ElasticSearch.
We also use ElasticPress as a WordPress plugin to talk to OpenSearch. However, ElasticPress currently assumes that it is talking to an ElasticSearch instance. Therefore, when OpenSearch reports back its version to ElasticPress, this causes issues as OpenSearch and ElasticSearch version numbers do not align.
This plugin hooks into ElasticPress to make it think a suitable ElasticSearch version number has been reported back, therefore causing ElasticPress to behave correctly.
See 10up's documentation of this issue, and our NAO PR when we first encountered this issue.