\documentclass[aspectratio=169,handout]{beamer}
\usepackage{pgfpages}
\pgfpagesuselayout{4 on 1}[a4paper,landscape,border shrink=5mm] % Use when printing handouts

\input{base.tex}
\input{theme.tex}
\input{content/content.tex}
\input{content/bibliography.tex}