If latex is TRUE and you render to PDF, LaTeX, or other output
formats requiring LaTeX (e.g., beamer_presentation, see knitr::is_latex_output),
a YAML metadata block with a header-includes argument calling the required
unicode-math LaTeX package is printed.
An RMarkdown file can only include one header-includes metadata entry. If
your document already has one, set latex to FALSE and manually add
add the unicode-math package to your LaTeX header instead.
(Note that header-includes is generally discouraged in favor of adding
an include argument to specific output formats, see
https://bookdown.org/yihui/rmarkdown/pdf-document.html#includes.)