Instead, the text version is displayed in less (I believe). However, I
have no issues to start the html help with the following.
starting httpd help server ... done
If 'xdg-open' is already running, it is *not* restarted, and you must
switch to its window.
Otherwise, be patient ...
The help page states:
"If for some reason HTML help is unavailable (see
?startDynamicHelp?), plain text help will be used instead."
However,
No documentation for 'startDynamicHelp' in specified packages and libraries:
you could try '??startDynamicHelp'