https://tex.stackexchange.com/q/553835/35864

secnamecap.tex

\listfiles
\documentclass{beamer}

\usepackage{textcase}

\makeatletter
\newcommand*{\orig@secname}{}

\defbeamertemplate*{section page}{mytemplate}{%
  \let\orig@secname\secname
  \expandafter\def\expandafter\secname\expandafter{%
    \expandafter\MakeTextUppercase\expandafter{\orig@secname}}%
  \insertsection}
\makeatother

\begin{document}
\section{Conclusions}
\frame{\sectionpage}
\end{document}