Hello, the LuaTeX manual PDF (version: February 14, 2021) as included on CTAN [1] and in TeX Live [2] is missing the luaharfbuzz reference. ConTeXt's grey placeholder is present instead. The older version (January 30, 2021) as present in the LuaTeX SVN repository [3] is fine in this regard. (The version present in ConTeXt is missing the chapter about HarfBuzz entirely, but I believe this is intentional.)
I am sorry if this isn't the right place or time for the report, but I am not sure how the is manual propagated and TeX Live freeze is near. Michal Vlasák [1] http://mirrors.ctan.org/systems/doc/luatex/luatex.pdf [2] https://tug.org/svn/texlive/trunk/Master/texmf-dist/doc/luatex/base/luatex.pdf?view=co [3] https://serveur-svn.lri.fr/svn/modhel/luatex/trunk/manual/luatex.pdf
