Just subscribe to communities located on programming.dev from here. Then when someone else with similar interests searches from here they'll see that community listed right away and can subscribe as well. You'll see the same content as if you were registered on their instance.
As for promoting, I know over on [email protected] they have a stickied post listing out all the dedicated team communities and instructions on subscribing. I've seen similar posts elsewhere. You may find some other related communities and make a post sharing that dataengineering community to drive some traffic to it.