The slanted lines are correct regarding the size of characters, but horizontal isn't. How to correct that ?
\documentclass{beamer}
\usepackage{fourier}
\usepackage{fontspec}
\setmainfont{Erewhon}[
Extension=.otf,
UprightFont=*-Regular,
ItalicFont=*-Italic,
BoldFont=*-Bold,
BoldItalicFont=*-BoldItalic,
SlantedFont=*-RegularSlanted,
BoldSlantedFont=*-BoldSlanted,
SmallCapsFont=*-SmallCaps,
SmallCapsFont=*-Regular,
SmallCapsFeatures={Letters=SmallCaps}
]
\setsansfont{texgyreheros}[
Scale=MatchLowercase,% or MatchUppercase
Extension=.otf,
UprightFont=*-regular,
ItalicFont=*-italic,
BoldFont=*-bold,
BoldItalicFont=*-bolditalic,
]
\usefonttheme{serif} % Nécessaire pour Fourier
\usepackage{ulem} % barrer des caractères
\begin{document}
\begin{frame}
{\Huge \xout{123} -- \sout{123}}
\end{frame}
\end{document}

