Open Area tab - and select Bitmap- click on Help button
Goes to Area tab help page
(There is a bitmap helppage: https://help.libreoffice.org/7.0/en-US/text/shared/01/05210500.html (but this page looks more like a stub for a Pattern help page, which does not exist, see bug #131403).
moving to NEW
Patch https://gerrit.libreoffice.org/c/help/+/96911 fixes it