There is no built-in option for unnumbered squares, but you can define your own version:

```
\documentclass{beamer}

\defbeamertemplate{section in toc}{square unnumbered}
{\leavevmode\raise0.1ex\hbox{\vrule width 1ex height 1ex}\kern1.25ex\inserttocsection\par}

\defbeamertemplate{subsection in toc}{square unnumbered}
{\leavevmode\leftskip=1.5em\raise0.2ex\hbox{\vrule width 0.9ex height 0.9ex}\kern1.25ex\inserttocsubsection\par}

\defbeamertemplate{subsubsection in toc}{square unnumbered}
{\leavevmode\leftskip=3em\raise0.3ex\hbox{\vrule width 0.8ex height 0.8ex}\kern0.75ex\inserttocsubsubsection\par}

\setbeamertemplate{sections/subsections in toc}[square unnumbered]

\begin{document}

\section{section name}  
\subsection{section name}
\subsubsection{section name}
\begin{frame}
 \tableofcontents
\end{frame}

\end{document}
```

![Screen Shot 2021-05-26 at 12.12.48.png](/image?hash=6ffe1c0800ee489cd78919f923faf150b31e2121ca4fc8949d2cedaa928e87e1)