Just as Kafka isn't a database, PostgreSQL isn't a queue/broker. You can use it that way, but you'll spend a lot of time tweaking it, and I suspect you'll find it's too slow for non-trivial workloads.
Skype at its earlier peak used Postgres as a queue at huge scale. PGQueue. It had a few tweaks and, sure, it is an anti-pattern but it can work. It is sure handy if you are already using postgres and want to maintain a small stack.