\documentclass[12pt]{article}

\usepackage{fontspec}
\usepackage{polyglossia}

\setlength{\textheight}{130mm}

\usepackage{makeidx}
\makeindex

\setdefaultlanguage{hungarian}
\setmainfont{Noto Serif}
\setsansfont{Noto Serif}

\pagestyle{empty}
\begin{document}
\thispagestyle{empty}

c\index{c}.
cr\index{cr}.
cs\index{cs}.
ct\index{ct}.
%d\index{d}.
dy\index{dy}.
dz\index{dz}.
dzr\index{dzr}.
dzs\index{dzs}.
dzt\index{dzt}.
dzz\index{dzz}.
e\index{e}.

o\index{o}.
ö\index{ö}.
ő\index{ő}.
u\index{u}.
ü\index{ü}.
ű\index{ű}.

\printindex

\end{document}


\index{}.