man rsync:

A trailing slash on the source changes this behavior to avoid creating
an additional directory level at the destination. You can think of a
trailing / on a source as meaning “copy the contents of this directory”
as opposed to “copy the directory by name”, but in both cases the
attributes of the containing directory are transferred to the contain‐
ing directory on the destination. In other words, each of the follow‐
ing commands copies the files in the same way, including their setting
of the attributes of /dest/foo: