As of version 2.3.7, Adobe Commerce supports Elasticsearch 7.9.3 but should work with 7.x. Support for Elasticsearch 6.x has been deprecated. Elasticsearch 2.x and 5.x have reached end-of-life and are no longer supported.
Change the Elasticsearch Client version
If you need to work with Elasticsearch 7.x, run the following command, specifying your desired version:
1 composer require "elasticsearch/elasticsearch:~7.1"
Then configure Elasticsearch within Magento Admin.