'Directly connected' to a project might mean a user of - but I assume you mean a major contributor to (as even small time users of free software often contribute something - bug reports, feature requests, code contributions, money, etc).

The page: https://pulsar.apache.org/powered-by/ suggests there's quite some number of corporate users who are happy to confirm they use this suite. I don't know how many of those you've heard of, though.

I suspect many private & government agencies around the world would decline to formally attach their name to any list like this, lest it be (mis)interpreted as an endorsement.

I've heard of Comcast, but that's Yahoo. Not heard of the others.