\documentclass{article}
\usepackage[a4paper]{geometry}
\pagestyle{empty}
%StartVisiblePreamble
\usepackage[DefaultFeatures={Scale=0.94}]{plex-otf}
%StopVisiblePreamble
\begin{document}
1/3 2/3 1/5 2/5 \ldots \par
\addfontfeatures{Fractions=On}
1/3 2/3 1/5 2/5 3/5 4/5 1/6 5/6 1/7 1/9 1/8 3/8 5/8 7/8\par
123456/3215731
\end{document}
