Compare the baseline alignment of integrals.
aka. What's up must come down.
\begin{document}
\use[module=packages.math]
\set[parameter=math.font.family,value=Libertinus Math]
\begin[mode=display]{math}
\sum_{k=0}^\infty \int_{0}^\infty e^{-kx^2}\,\mo{d}x
\end{math}
\end{document}
sile -o integral-alignment-sile.pdf integral-alignment-sile.sil
\documentclass{article}
\usepackage{unicode-math}
\setmathfont{Libertinus Math}
\begin{document}
\[
\sum_{k=0}^\infty \int_0^\infty e^{-kx^2}\,\symup{d}x
\]
\end{document}
xelatex -interaction=batchmode -halt-on-error -jobname data/integral-alignment-xelatex integral-alignment-xelatex.tex