Crunchydata mentioned it on their blog a while back (https://www.crunchydata.com/blog/five-tips-for-a-healthier-p...) and the pg 14 release notes mention a few changes to idle sessions (https://www.postgresql.org/docs/release/14.0/)
I don't know if they were sufficient that pgbouncer is no longer necessary, haven't had a need to try it.