Changing document font family

[e-duckworth]

I'm probably missing something, I don't seem to be able to change the document font with e.g. \usepackage{charter} or \usepackage{mlmodern}. In addition, when I do run one of these backages, I lose the ability to set strongEmphasis. E.g. the following

\usepackage{charter}
\usepackage{markdown}
\markdownSetup{
 renderers = {
    emphasis = {\emph{#1}},
    strongEmphasis = {\textbf{#1}},
  },
}
\begin{document}
\begin{markdown}
Test **OTB**
\end{markdown}

doesn't produce OTB in bold, nor does it use charter.

[Witiko]

If I enclose your example document with \documentclass{article} on top and \end{document} at the bottom and change the text between \begin{markdown} and \end{markdown} to foo _bar_ **baz**, I receive the following output with pdfLaTeX from TeX Live 2024:

With LuaLaTeX, I receive the following output instead:

Therefore, my hunch is that you are trying to use the package charter with LuaLaTeX, which is apparently not supported.

Regardless, this has nothing to do with the Markdown package, it is the usual LaTeX jank.

[e-duckworth]

Thank you, I didn't realize the conflict with lualatex.