Since outline folding feature is no longer experimental (see bug 14820), help page  needs an update.
Patch submitted here: https://gerrit.libreoffice.org/c/help/+/132375
Julien Nabet committed a patch related to this issue.
It has been pushed to "master":
tdf#148302: Outline folding no more experimental
VERIFIED, see https://help.libreoffice.org/7.4/en-US/text/swriter/01/outlinecontent_visibility.html?&DbPAR=WRITER&System=WIN
Julien, thanks for fixing it!