\documentclass{beamer}
\begin{document}
\begin{frame}
  \begin{columns}
    \begin{column}[c]{0.5\linewidth}
      Test
    \end{column}
    \fbox{\begin{column}[c]{0.5\linewidth}
        \begin{itemize}
        \item test
        \end{itemize}
      \end{column}}
  \end{columns}
\end{frame}
\end{document}

\documentclass{article}
\usepackage{tabularray}

\begin{document}

\begin{tblr}{}
 \SetRow{cmd={\def\duck{quack}}} a & \duck\\
\end{tblr}

\end{document}