Voici une idée basée sur l'utilisation de la bibliothèque `magazine` de *tcolorbox*
\documentclass{article}
\usepackage{lmodern}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{multicol}
\usepackage[most]{tcolorbox}
\usepackage{mwe}
\newcounter{mtctr}
\newcommand{\mtdisplay}{%
\boxarraygetsize{\mtsize}%
\setcounter{mtctr}{0}%
\loop
\stepcounter{mtctr}%
\tcbitem\consumeboxarray{\themtctr}
\ifnum\value{mtctr}<\mtsize
\repeat}
\newcommand{\mtdim}{%
\the\dimexpr\pagegoal-\pagetotal-1cm\relax/
\the\dimexpr\pagegoal-\pagetotal-1cm\relax/
\the\dimexpr\textheight-1cm\relax}
\newenvironment{mttwocols}{%
\ifdim\dimexpr\pagegoal-\pagetotal-6\baselineskip\relax>0pt\else\newpage\null\vskip-\baselineskip\fi
\begin{tcolorbox}[%
breakable,
blanker,
width=.43\textwidth,
break at=\mtdim,
reset box array,
store to box array]}{%
\end{tcolorbox}
\tcboxeditemize[%
blanker,
sharp corners,
halign=center,
raster columns=2,
raster valign=top]{breakable}%
\mtdisplay
\endtcboxeditemize}
\begin{document}
\section{Foo}
\lipsum[1]
\begin{mttwocols}
\lipsum[1-20]
\end{mttwocols}
\end{document}
Pour aller plus loin
loin.
**Remarques** il faut compiler deux fois et il faut supprimer le fichier `.aux` en cas des changements dans `mttwocols`.
**Limitation** `mttwocols` à utiliser une fois par fichier, mais ce n'est pas difficile d'adapter le code pour l'utilisation multiple, je vais essayer d'ajouter ce qu'il faut prochainement.
\documentclass{article}
\usepackage{lmodern}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{multicol}
\usepackage[most]{tcolorbox}
\newcounter{mtctr}
\newcommand{\mtdisplay}{%
\boxarraygetsize{\mtsize}%
\setcounter{mtctr}{0}%
\loop
\stepcounter{mtctr}%
\tcbitem\consumeboxarray{\themtctr}
\ifnum\value{mtctr}<\mtsize
\repeat}
\AtBeginDocument{
\providecommand{\mtdim}{%
\the\dimexpr\pagegoal-\pagetotal-1cm\relax/
\the\dimexpr\pagegoal-\pagetotal-1cm\relax/
\the\dimexpr\textheight-1cm\relax}}
\makeatletter
\newcommand{\mtsetdim}{%
\renewcommand{\mtdim}{%
\the\dimexpr\pagegoal-\pagetotal-1cm\relax/
\the\dimexpr\pagegoal-\pagetotal-1cm\relax}
\boxarraygetsize{\mtsize}
\global\let\mtsize\mtsize
\boxarraygetbox{\mtbox}{\mtsize}
\ifnum\mtsize>2
\setcounter{mtctr}{3}
\loop
\ifnum\value{mtctr}<\numexpr\mtsize-1\relax
\xdef\mtdim{\mtdim/ \the\dimexpr\textheight-1cm\relax}
\stepcounter{mtctr}
\repeat
\ifodd\value{mtctr}
\xdef\mtht{\the\dimexpr.5\textheight+.5\ht\mtbox+\baselineskip\relax}
\else
\xdef\mtht{\the\dimexpr\textheight-1cm\relax/\the\dimexpr.5\ht\mtbox+\baselineskip\relax}
\fi
\xdef\mtdim{\mtdim/ \mtht}
\fi
\immediate\write\@mainaux{\xdef\string\mtdim{\mtdim}}
}
\makeatother
\newenvironment{mttwocols}{%
\ifdim\dimexpr\pagegoal-\pagetotal-6\baselineskip\relax>0pt\else\newpage\null\vskip-\baselineskip\fi
\begin{tcolorbox}[%
breakable,
blanker,
width=.43\textwidth,
break at=\mtdim,
reset box array,
store to box array]}{%
\end{tcolorbox}
\mtsetdim
\tcboxeditemize[%
blanker,
sharp corners,
halign=center,
raster columns=2,
raster valign=top]{breakable}%
\mtdisplay
\endtcboxeditemize}
\usepackage{mwe}
\begin{document}
\section{Foo}
\lipsum[1]
\begin{mttwocols}
\lipsum[1-20]
\end{mttwocols}
\end{document}\end{document}
