The Elasticsearch-centric docs for upgrades are here. You can indeed start a 7.6.0 node on top of data from a 7.5.0 node and let Elasticsearch handle the upgrade automatically, so there's no need to regenerate anything or worry about schema changes.
Unfortunately I don't know how to translate this into the changes you need for your docker-compose.yml, but note that the section on preparing to upgrade says:
- Test the upgrade in an isolated environment before upgrading your production cluster.
Please do this!