I also would love for Zammad to support Opensearch. From what I tried, it looks like it checks and refuses to talk to anything that is not Elasticsearch. I don’t think that should end up in a final error, but a warning.
Also, it seems like the Debian package depends on elasticsearch|elasticsearch-oss. If Opensearch is supported (or even merely ‘tolerated’), that should change to elasticsearch|elasticsearch-oss|opensearch, and remove, make optional, or update the configuration of elasticsearch that the installation script performs to use the adequate binary if Opensearch is used.
You can workaround that by creating a dummy package, that provides elasticsearch:
Prepare the directory:
create a file elasticsearch-dummy with content
Version: 2.3.0-1 # or whatever you want
Maintainer: Your Name <firstname.lastname@example.org>
Description: Dummy package for ElasticSearch server
Dummy package for ElasticSearch server to satisfy dependencies of Zammad package.
This is a feature request post, please try to keep it clean with request related content. While it might help OP to make it run, OpenSearch is still not officially supported and this is what this request is about.