How to center sections and subsections in beamer using \tableofcontents

Question

How do I center (or even just simply increase the left margin of) the outline produced by \tableofcontents in beamer?

Normal tools like \centering or \begin{center}..\end{center} do not work because the list should be left-aligned, but appearing in the center.

Environments like minipage, columns also do not work because, as mentioned in this answer, beamer collapses the vertical spacing.

The proposed solution in the linked answer also doesn't work because subsection bullets, for some reason, are oblivious to the \leftskip parameter.

Thank you!

MWE:

\documentclass[xelatex, aspectratio=169, 10pt]{beamer}
\begin{document}
\begin{frame}{Outline}
  %\begin{columns}[c]
    %\begin{column}{0.9\textwidth}
      \setlength{\leftskip}{0.1\textwidth}
      \setbeamertemplate{section in toc}[sections numbered]
      \setbeamertemplate{subsection in toc}[subsections numbered]
      \tableofcontents
    %\end{column}
  %\end{columns}
\end{frame}
\section{Intro section}
\subsection{Case alpha}
\begin{frame}
  Frame 1
\end{frame}
\subsection{Case beta}
\begin{frame}
  Frame 2
\end{frame}
\section{Results}
\subsection{First experiment}
\begin{frame}
  Frame 3
\end{frame}
\subsection{Second experiment}
\begin{frame}
  Frame 4
\end{frame}
\subsection{Third experiment}
\begin{frame}
  Frame 5
\end{frame}
\end{document}

Answer 1

You could add a bit of horizontal space to the subsection in toc template:

\documentclass[aspectratio=169, 10pt]{beamer}
\begin{document}
\begin{frame}{Outline}
  %\begin{columns}[c]
    %\begin{column}{0.9\textwidth}
      \setlength{\leftskip}{0.4\textwidth}
      \setbeamertemplate{section in toc}[sections numbered]
      \setbeamertemplate{subsection in toc}[subsections numbered]
      \addtobeamertemplate{subsection in toc}{\hspace{.4\textwidth}}{}
      \tableofcontents
    %\end{column}
  %\end{columns}
\end{frame}
\section{Intro section}
\subsection{Case alpha}
\begin{frame}
  Frame 1
\end{frame}
\subsection{Case beta}
\begin{frame}
  Frame 2
\end{frame}
\section{Results}
\subsection{First experiment}
\begin{frame}
  Frame 3
\end{frame}
\subsection{Second experiment}
\begin{frame}
  Frame 4
\end{frame}
\subsection{Third experiment}
\begin{frame}
  Frame 5
\end{frame}
\end{document}