Beamer stop slide numbering after some slides

Question

OK, I have put some pretty nice slides for my forthcoming conference paper presentation. I used the slide numbering format SLIDE No./TOTAL SLIDES. But I added some backup slides to help answer potential questions at the end of my presentation (after the Conclusion slide).

So I want the slide numbering to stop at the conclusion slide since those backup slides are not part of my talk.

MWE:

\documentclass{beamer}
\usepackage[utf8]{inputenc}
\usetheme{Madrid}
\usepackage{lipsum}

\title[BAU] 
{Here's my paper title}

\author[F.~Author, S.~Author \& L.~Author] 
{F.~Author\inst{1} S.~Author\inst{1,}\inst{2} \and L.~ Author\inst{1,}\inst{3}}

\institute[BAU] 
{
  \inst{1}%
    The University
  \and
  \inst{2}%
    Institute ABC
  \and
  \inst{3}%
  Lab XYZ
}

\date[PQR 2021] 
{PQR2021  \\September 19-22, 2021
 }

\setbeamertemplate{caption}{\raggedright\insertcaption\par}

\begin{document}

\frame{\titlepage}

\begin{frame}{Introduction}
    
    \lipsum[1][1]\par
    \lipsum[1][2]\par
    \lipsum[1][3]\par
    
\end{frame}


\begin{frame}[allowframebreaks]{Methodology}
   \lipsum[1][4-6]\par
\end{frame}

\begin{frame}[allowframebreaks]{Data Collection}
    \lipsum[2-4][12-18]\par
        
        \framebreak
        \lipsum[1][4]\par
        \lipsum[1][5]\par
        \lipsum[1][6]\par
\end{frame}

\section{Conclusion }% 
   \begin{frame}{Conclusion}
      \begin{itemize}
      \setlength\itemsep{1em}
          \item Some points.
          \item More points.
          \item Yet even more points.
      \end{itemize}
       
   \end{frame}

\begin{frame}[allowframebreaks]{Backup Slide}
    \textbf{Figure to ans potential question}
    
    \framebreak
    \textit{Table XXX}
\end{frame}

\end{document}

In this case, the Conclusion slide number should be 6/6 not 6/8.

Answer 1

You can put additional material (backup slides) in appendix and add \setbeamertemplate{page number in head/foot}[appendixframenumber] in the preamble. Appendix will then use its own numbering.

\documentclass{beamer}
\usepackage[utf8]{inputenc}
\usetheme{Madrid}
\usepackage{lipsum}

\title[BAU] 
{Here's my paper title}

\author[F.~Author, S.~Author \& L.~Author] 
{F.~Author\inst{1} S.~Author\inst{1,}\inst{2} \and L.~ Author\inst{1,}\inst{3}}

\institute[BAU] 
{
  \inst{1}%
    The University
  \and
  \inst{2}%
    Institute ABC
  \and
  \inst{3}%
  Lab XYZ
}

\date[PQR 2021] 
{PQR2021  \\September 19-22, 2021
 }

\setbeamertemplate{caption}{\raggedright\insertcaption\par}
\setbeamertemplate{page number in head/foot}[appendixframenumber]

\begin{document}

\frame{\titlepage}

\begin{frame}{Introduction}
    
    \lipsum[1][1]\par
    \lipsum[1][2]\par
    \lipsum[1][3]\par
    
\end{frame}


\begin{frame}[allowframebreaks]{Methodology}
   \lipsum[1][4-6]\par
\end{frame}

\begin{frame}[allowframebreaks]{Data Collection}
    \lipsum[2-4][12-18]\par
        
        \framebreak
        \lipsum[1][4]\par
        \lipsum[1][5]\par
        \lipsum[1][6]\par
\end{frame}

\section{Conclusion }% 
   \begin{frame}{Conclusion}
      \begin{itemize}
      \setlength\itemsep{1em}
          \item Some points.
          \item More points.
          \item Yet even more points.
      \end{itemize}
       
   \end{frame}

 \appendix
   
\begin{frame}[allowframebreaks]{Backup Slide}
    \textbf{Figure to ans potential question}
    
    \framebreak
    \textit{Table XXX}
\end{frame}

\end{document}

Answer 2

Thank you \usepackage{appendixnumberbeamer} package is what I need, then add the command \appendix just before the backup slides.