\documentclass[9pt]{extarticle}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage[ngerman]{babel}
%\usepackage[english]{babel}
\usepackage{titlesec}
\usepackage{enumitem}
\usepackage{cancel}
\usepackage{multicol}
\usepackage{yfonts}
\usepackage{appendix}
\usepackage{mathtools}
\usepackage{bm}
\usepackage{esvect}
\usepackage{graphicx}
%\graphicspath{{images/}{../images/}}
\usepackage[boxsize=4pt]{ytableau}
\usepackage{subfiles}
\usepackage{blindtext}
\usepackage{subfiles}
\usepackage{breqn}
\usepackage{geometry}
\usepackage{sectsty}
\usepackage[boxsize=2]{ytableau}
\usepackage{bbold}

\geometry{a4paper,
left=5mm,right=5mm,
top=5mm,bottom=5mm
}

%\titleformat{\section}{\large\bfseries}{\thesection}{1em}{}
%\titleformat{\subsection}{\bfseries}{\thesection}{1em}{}

\setlength{\parindent}{0pt}
\setlist[itemize]{itemsep=-3pt,topsep=-1pt,leftmargin=*}%Damit die listen kleiner werden
\sectionfont{\fontsize{12}{15}\selectfont}

\title{<++>}

\author{Alexander Bocken}

\date{<++>\\Version \today}

\renewcommand{\thefootnote}{}

\begin{document}

\maketitle
\tableofcontents
\thispagestyle{empty}

\end{titlepage}

\setcounter{section}{0}

\begin{multicols}{3}

\section{<++>}

\subfile{Kapitel/<++>}

\appendix

\section{{<++>}

\subfile{Appendix/<++>}

\end{multicols}
\end{document}