\DocumentMetadata{}
\ExplSyntaxOn
\pdfmanagement_add:nnn { Page / Resources / ExtGState } { lvd } { << /ca~0.5 /CA~0.5 >> }
\ExplSyntaxOff
\documentclass[border=5pt]{standalone}
\usepackage{lua-visual-debug}
\usepackage{unicode-math}
\lvdset{
  glyph = {color={0 0 1 RG} width=0.12} 
  onlyglyphs
  opacity = {/lvd gs}
}
\begin{document}
This is an example $\intop_a^b f(x) dx$
\end{document}