(This isn’t actually a question, but just an anchor for the answer I want to give.)
Over years similar questions were posted in different places as well in this site as in different ones (like the PortableApps forum).
Also here and in different places I posted a link to a rather wordy, but hopefully clear instruction how to get that help. Now this link is broken, and I upload the most recent version of the instruction here as my answer.
Read the attached PDF:
LibOPortableOfflineHelp.pdf (76.4 KB)
The link at the end points to the discussion in the PortabelApps help forum, but the secondary link contained in my post there is broken as already mentioned.
Please note: For a long time now, the offline help consists of html files using the default browser of your system to display the content. If something doesn’t work as expected, the browser configuration may be the cause. Such an issue isn’t a LibO one.