As seen in bug 124298, this needs to be documented to avoid confusions.
I have added some content to the LibreOffice 6.3 Release Notes regarding this feature: https://wiki.documentfoundation.org/ReleaseNotes/6.3#New_Feature:_Redaction I tried to make it usable also as a user documentation, and ref for help pages. @olivier: Maybe we can add it to 6.3 user guides?
To help to fix this bug: Please follow the instructions of https://documentation.libreoffice.org/en/join-the-documentation-team/update-help-contents/ in "The easy way" section. Use wiki page contents indicated in comment#0. Plenty of info.
Olivier Hallot committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/help/+/965724a89fb88f693e85da64a1e8b6a1556d373c%5E%21 tdf#124299 Redaction Help page
A polite ping to Olivier Hallot, Is this bug fixed? if so, could you please close it as RESOLVED FIXED ? Otherwise, Could you please explain what's missing? Thanks