Millions of events per day is still in the small queue category in my book. Postgres LISTEN doesn't scale, and polling on hot databases can suddenly become more difficult, as you're having to throw away tuples regularly.

10 message/s is only 860k/day. But in my testing (with postgres 16) this doesn't scale that well when you are needing tens to hundreds of millions per day. Redis is much better than postgres for that (for a simple queue), and beyond that kafka is what I would choose in you're in the low few hundred million.