PSA: With macOS 15 Sequoia (released in September 2024), Apple has started shipping openrsync (created by Kristaps Dzonsons, from OpenBSD) as an alternative to the original rsync (“tridge”, from the Samba project).

When you run “rsync”, a wrapper will inspect your command and dispatch to either /usr/libexec/rsync/rsync.samba or rsync.openrsync: https://github.com/apple-oss-distributions/rsync/blob/main/rsync.wrapper.c

If you need one version over the other, select them explicitly — and probably rsync.samba will disappear eventually…