\documentclass{beamer}
\usetheme{default}
\usepackage{ucs}
\usepackage[utf8x]{inputenc}
\usepackage[greek,english]{babel}
\newcommand{\en}{\selectlanguage{english}}
\newcommand{\gr}{\selectlanguage{greek}}

\begin{document}
	\en
\title{Put your title here}
\author{Author 1  Author 2}
\institute{Department of Economics \\ University of Patras \\ University Campus, Rio, 26504, Patras}
\date{October 2023}

	
\begin{frame}
	\maketitle
\end{frame}

\begin{frame}
\begin{itemize}
	\item cvxvxcv {\gr καλημέρα} df  sad sa
	\item cvxvxcv
	\item cvxvxcv
	\item cvxvxcv
\end{itemize}
\end{frame}

\begin{frame}
\begin{itemize}
	\item cvxvxcv
	\item cvxvxcv
	\item cvxvxcv
	\item cvxvxcv
\end{itemize}
\end{frame}

\end{document}