\documentclass{thesis}
\newcommand{\thesistitle}{TODO TITLE}
\usepackage{mathpazo}  % font: palatino vs computer modern
\usepackage{lipsum} % used to fill random text in sections
\usepackage{tikz} % used for sample figure
\newenvironment{dedication}
  {%\clearpage           % we want a new page          %% I commented this
   \thispagestyle{empty}% no header and footer
   \vspace*{\stretch{1}}% some space at the top
   \itshape             % the text is in italics
   \raggedleft          % flush to the right margin
  }
  {\par % end the paragraph
   \vspace{\stretch{3}} % space at bottom is three times that at the top
   \clearpage           % finish off the page
  }
\begin{document}
    % Titlepage (empty pagestyle)
    % Contains titlepage, empty page, "Prodekan + Doktorvater", empty page
    \pagestyle{empty}
    \pagenumbering{gobble}
    \input{titlepage.tex}
    \input{chapters/Dedication}
    \cleardoublepage
    \tableofcontents
    \cleardoublepage
    \pagestyle{fancy}
    \setcounter{tocdepth}{2}
    \frontmatter
    \setcounter{page}{1}
    % Add acronyms from file (_Acronyms.tex) and add to table of contents
    \input{chapters/Acronyms}
    % Add list of figures and list of tables
    \newpage
    \phantomsection
    \addcontentsline{toc}{chapter}{List of Figures}
    \listoffigures
    \listoftables
    \addcontentsline{toc}{chapter}{List of Tables}
    \mainmatter
    
    
    \mainmatter
    % % Main Body of thesis
    \input{chapters/01_Introduction/00}
    \input{chapters/02_Materials_and_Methods/00}
    \input{chapters/03_Results/00}
    \input{chapters/04_Discussion/00}
    \input{chapters/05_Summary}
    \input{chapters/06_Zusammenfassung}
    
    \clearpage
    \phantomsection
    \addcontentsline{toc}{chapter}{Bibliography}
    \markboth{Bibliography}{Bibliography}
    \bibliography{refs} % In overleaf you can link to Zotero. Go to "new file"->"From Zotero"
    \input{chapters/07_Own_Publications}
    \pagestyle{plain}
    % Include CV from PDF like this:
    \phantomsection
    \addcontentsline{toc}{chapter}{Curriculum Vitae}
    \includepdf[pages=-,frame,scale=.77,pagecommand={\thispagestyle{plain}}]{figures/CV.pdf}
    
    \input{chapters/08_Appendix}
    \input{chapters/09_Acknowledgement}
    \input{chapters/10_Eidestattliche_Erklärung}
    \input{chapters/11_Angabe_KI}
\end{document}