A heavily modified LaTex template file for Xournal++, bypassing the forced math mode and unlocking full LaTex embedding potential. See https://github.com/xournalpp/xournalpp/blob/master/resources/default_template.tex for comparison.

latex_template.tex

% This template uses the scontents package, which is only available on relatively recent TeX distributions.
% In case it is not available on your system, use the legacy_template.tex
\documentclass[varwidth=500pt, border=2pt]{standalone}

%% Global Packages ------------------------------------------------------------
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{textgreek}
\usepackage{siunitx}

% Math packages
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{pgfplots}

% Chemistry packages
\usepackage[version=4]{mhchem}
\usepackage{chemfig}
\usepackage[minimal]{chemmacros}
\usetikzlibrary{calc}


%% Chemistry Macros -----------------------------------------------------------
% Orbital box notation
\newcommand{\orbox}[2]{
  \newcommand*{\up}{%
    \fbox{\( \mathord\upharpoonleft\phantom{\downharpoonright} \)}%
  }%
  \newcommand*{\down}{%
    \fbox{\( \mathord\downharpoonleft\phantom{\upharpoonright} \)}%
  }%
  \newcommand*{\updown}{%
    \fbox{\( \upharpoonleft\downharpoonright \)}%
  }%
  \newcommand*{\blank}{%
    \fbox{\( \phantom{\downharpoonright}\phantom{\downharpoonright} \)}%
  }%
  \setlength\tabcolsep{0pt}% remove extra horizontal space from tabular
  \begin{tabular}{c}%
    #2 \\
    [2pt]#1%
  \end{tabular}
}

% Default settings for drawing Lewis structure
\setcharge{
  extra sep=0.3em,
  .radius=0.2ex,
  .style={fill=blue,draw=none}
}

%% Mathematics Macros ---------------------------------------------------------
% Enter aligned equation environment quickly
\newcommand{\aln}[1]{%
  \[%
  \begin{aligned}%
    #1%
  \end{aligned}%
  \]%
}

% Auto-size bracket
\newcommand*{\brc}[1]{%
  \left(#1\right)%
}

% Long division
\newcommand*{\longdiv}[1]{%
  \strut#1%
  \kern.25em%
  \smash{ \hbox{\big)} }%
  \mkern-8mu%
}

% Plot function graphs
\pgfplotsset{compat=newest} % Allows to place the legend below plot
\NewDocumentCommand{\graph}{O{} O{} m}{
  \begin{tikzpicture}
  \begin{axis}[
    xlabel=$x$,
    ylabel=$y$,
    axis lines=center,
    samples=100,
    \IfBlankF{#1}{#1}
  ]
    \addplot[]{#3};
  \end{axis}
  \end{tikzpicture}
}

% Nicely formatted definite integrals
\NewDocumentCommand{\intf}{o o m O{x}}{
  \int%
  \IfValueT{#1}{_{#1}}
  \IfValueT{#2}{^{#2}}
  #3 \mathop{}\!
  \mathrm{d}#4
}
\newcommand*{\intb}[3]{
  \left[ #3 \right]_{#1}^{#2}
}

% Combination and permutation
\newcommand*{\nPr}[2]{
  {}^{#1}\!P_{#2}
}
\newcommand*{\nCr}[2]{
  {}^{#1}C_{#2}
}


%% Xournal++ default_template.tex ---------------------------------------------
% for storing in memory verbatim content to be reused later
\usepackage{scontents}

% Color support
\usepackage{xcolor}
\definecolor{xpp_font_color}{HTML}{%%XPP_TEXT_COLOR%%}

% User input
\begin{scontents}[store-env=preview]
  %%XPP_TOOL_INPUT%%
\end{scontents}

\begin{document}
  % Render the user input
  \textcolor{xpp_font_color}{\getstored[1]{preview}}
\end{document}