\documentclass[11pt, a4paper, twoside]{article}
\usepackage[
    a4paper,
    headsep=5mm,
    footskip=0mm,
    top=12mm,
    left=10mm,
    right=10mm,
    bottom=10mm
]{geometry}
\usepackage{amsmath}
\usepackage{gauss}
\usepackage{nicematrix}
\usepackage{tikz}
\usepackage{amsfonts}
\usepackage{makecell}
\usepackage{multicol}
\usepackage[noend]{algorithm2e}
\usepackage[utf8]{inputenc}
\usepackage{fancyhdr}
\usepackage{tikz}
\usetikzlibrary{arrows,automata,positioning, graphs, graphdrawing}
\usegdlibrary {trees} 
\usepackage{hyperref}
\hypersetup{
    colorlinks=true,
    linkcolor=blue,
    filecolor=magenta,      
    urlcolor=cyan,
    pdftitle={Overleaf Example},
    pdfpagemode=FullScreen,
    }

\setlength{\algomargin}{0pt}

\begin{document}
\pagestyle{fancy}
\fancyhead{}
\fancyhead[L]{Mein tolles Modul}
\fancyhead[R]{Gero Beckmann - \url{https://github.com/Geronymos/}}
\fancyfoot{}
\fancyfoot[R]{\thepage}
\newenvironment{definition}[1]{\noindent\textbf{#1:}}{}
\section{Deine Überschrift}

Hier könnte ihr Text stehen.

\end{document}