\KOMAoption{chapterprefix}{true}
\renewcommand*\raggedchapter{\centering}
\RedeclareSectionCommand[
  beforeskip=0pt,
  innerskip=-.3\baselineskip,
  %afterskip=8\baselineskip,
  font=\Huge\sffamily,
  prefixfont=\normalfont\large\scshape
]{chapter}

\renewcommand*{\chapterformat}{%
  \chapappifchapterprefix{\nobreakspace}\thechapter\autodot%
  \IfUsePrefixLine{%
    \par\nobreak\vspace*{-\parskip}\vspace*{-.6\baselineskip}%
    \rule{0.9\textwidth}{.5pt}%
  }{\enskip}%
}

\renewcommand\chapterlineswithprefixformat[3]{%
  \ifstr{#2}{}{%
    % For unnumbered chapters (aronyms and bibliography): flush chapter titles to the left
    \flushleft#2#3%
  }{%
    % For numbered chapters (introduction, main, conclusion, aso.): make the chapter titles uppercase and add some bottom margin
    #2\MakeUppercase{\textls[120]{#3}}%
    \vspace*{50pt}%
  }%
}