How do I find out what changed for an freebsd release update?

From: Rick Macklem <rmacklem_at_uoguelph.ca>
Date: Fri, 15 Oct 2021 23:48:01 UTC
Hi,

PR#259163 reports a problem w.r.t. the NFSv3 server that surfaced when
the server was upgraded from 12.2-p8 to 12.2-p9.
I know that nothing changed in NFS server code, but how can I find out
what did get changed by that update?

Thanks in advance for any help, rick