in general you should be able to call an application named foo.exe from powershell by either writing foo or foo.exe (i briefly tested this with another application).
however, i just realised something: opensearch doesn’t seem to have a windows binary release yet, so you don’t have any opensearch-plugin.exe available (and opensearch-plugin is a linux binary): [Meta] OpenSearch / OpenSearch Dashboards - Windows distribution (X64) · Issue #33 · opensearch-project/opensearch-build · GitHub