`∗` (unicode U+2217) n'est pas la même chose que `*` (unicode U+002A) :
% !TeX TS-program = lualatex
\documentclass{article}%
\documentclass{article}
\ExplSyntaxOn
\NewDocumentCommand{\geoPaperwidth}{}{148}%
\NewDocumentCommand{\geoPaperwidth}{}{148}
\NewDocumentCommand{\geoMarginLeftRight}{}{\fpeval{round(0.25 * \geoPaperwidth{},3)}}%
\geoPaperwidth{},3)}}
\NewDocumentCommand{\geoLeft}{}{\fpeval{round(0.6 * \geoMarginLeftRight{},3)}}%
\geoMarginLeftRight{},3)}}
\ExplSyntaxOff
\begin{document}%
\ExplSyntaxOn
\begin{document}
geoMarginLeftRight = \geoMarginLeftRight \\
\geoMarginLeftRight
geoLeft = \geoLeft%
\geoLeft
\ExplSyntaxOff
\end{document}%\end{document}
