V18.104.22.168(RC) as any RC is no longer a Dev version. Dev versions are installed separately in parallel by default, Release Candidates and released versions are installed to the default path if not special measures are taken.
Concerning parallel installations see this wiki page.
In any case you need to install the offline help for the used UI language(s) in addition.
You are on Windows? Any installation of Libreoffice has an executable
soffice.exe then in a specific folder which should be named
program. In the same folder as
program there should also be a folder
help. There you can have one tree of subfolders and files per Language/Country. In my case e.g. those are
en-US. LibO will use the one matching the current setting for its UI-language if present. It will shift to th online help system if it misses the matching folder.
The msi installer for a help package will place the tree into the path associated with the version installed in the standard way, not as a parallel version. How you can extract the tree to an explicitly given location in the file system, I described for the PortableApps versions here. It also applies to any parallel version. Just replace 32-bit help msi by the 64-bit version if applicable. Bit-width must match, I think.
Do not delete the files basically contained in the
help folder. They are needed for online help.