xsim Übung + Lösung + zusätzlich Kurzlösung?

\usepackage{environ,etoolbox}
\NewEnviron{shortsolution}{\SetExpandedExerciseProperty{shortsolution}{\expandonce{\BODY}}}

\NewDocumentEnvironment{shortsolution}{+b}
  {\SetExpandedExerciseProperty{shortsolution}{#1}}
  {}

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[no-files]{xsim}

\usepackage{needspace}

\DeclareExerciseProperty{shortsolution}

% we'll use a description list for the shortsolutions:
\makeatletter
\NewDocumentCommand\printshortsolutions{}{%
  \def\shortsolitems{}%
  \ForEachUsedExerciseByType{%
    \def\ExerciseType{##1}%
    \def\ExerciseID{##2}%
    \GetExercisePropertyT{shortsolution}
      {\g@addto@macro\shortsolitems{\unexpanded{\item[Short Solution ##3] ####1}}}%
  }%
  \XSIMifblankF\shortsolitems{%
    \begin{description}
      \shortsolitems
    \end{description}
  }%
}
\makeatother

\NewDocumentEnvironment{shortsolution}{+b}
  {\SetExpandedExerciseProperty{shortsolution}{#1}}
  {}

\begin{document}

\section{Problems}
% set shortsolution through option:
\begin{exercise}[subtitle=Pythagoras]
  This is the first problem.
  \begin{shortsolution}
    This is a shortsolution to the first problem.
  \end{shortsolution}
\end{exercise}
\begin{solution}
  This is the solution to the first problem.
\end{solution}

\begin{exercise}[subtitle=Another Problem]
  This is the second problem.
\end{exercise}
\begin{solution}
  This is the solution to the second problem.
\end{solution}

% set shortsolution with custom command:
\begin{exercise}[subtitle=Yet Another Problem]
  This is the third problem.
  \begin{shortsolution}
    This is a shortsolution to the third problem.
  \end{shortsolution}    
\end{exercise}
\begin{solution}
  This is the solution to the third problem.
\end{solution}

\section{Shortsolutions}
\printshortsolutions

\section{Solutions}
\printsolutions[headings=false]

\end{document}