During the release pipeline,
after the artifacts are staged,
send a notification with the optaplanner-distribution.zip, optaweb zips, and a link to the sanity checks process
to
A) zulip topic "sanity checks" on #optaplanner-dev
B) zulip CI topic + cc everybody in optaplanner team
C) mail (like 7.x)

Either of these 3 options is fine. I prefer A).