Credit to @Max C for simplifying the mwe:
Compiled with latexmk -lualatex
\DocumentMetadata{pdfstandard=ua-2, tagging=on, lang=en} \documentclass{book} \usepackage{mathtools, unicode-math} \begin{document} \begin{tabular}{l} \(a\) \end{tabular} \end{document}Package unicode-math Warning: Using \overbracket and \underbracket from(unicode-math) `mathtools' package.(unicode-math) (unicode-math) Use \Uoverbracket and \Uunderbracket for(unicode-math) original `unicode-math' definition.Package unicode-math Warning: I'm going to overwrite the following commands(unicode-math) from the `mathtools' package: (unicode-math) (unicode-math) \dblcolon, \coloneqq, \Coloneqq, \eqqcolon.(unicode-math) (unicode-math) (unicode-math) Note that since I won't overwrite the other(unicode-math) colon-like commands, using them will lead to(unicode-math) inconsistencies.\g__math_luamml_iow=\write3\openout3 = mwe-luamml-mathml.htmlPackage tagpdf Info: luamml has been enabled and will create an MathML file.WARNING: mathml missing for hash 44BC9D542A92714CAC84E01CBBB7FD61====>grabbed math=macro:->a