The following is a mix and revamp of the code for the article and report classes \part macro.
% partprob.tex SE 592540
\documentclass{article}
\makeatletter
\renewcommand{\part}{% % rejig of report/book \part
\clearpage
\thispagestyle{plain}
\if@twocolumn
\onecolumn
@tempswatrue
\else
@tempswafalse
\fi
\null\vfil
\secdef@part@spart}
\def@part[#1]#2{% % mixture of article and report/book code
\ifnum \c@secnumdepth >\m@ne
\refstepcounter{part}%
\addcontentsline{toc}{part}{\thepart\hspace{1em}#1}
\else
\addcontentsline{toc}{part}{#1}%
\fi
\markboth{}{}%
\vfil
{\centering
\interlinepenalty @M
\normalfont
\ifnum \c@secnumdepth >-1\relax
\huge\bfseries \partname\nobreakspace\thepart
\par
\vskip 20\p@
\fi
\Huge \bfseries #2\par}%
@endpart}
\def@spart#1{%
{\centering
\interlinepenalty @M
\normalfont
\Huge \bfseries #1\par}%
@endpart}
\def@endpart{\vfil\newpage
\if@twoside
\fi
\if@tempswa
\twocolumn
\fi}
\makeatother
\begin{document}
\part{First Part}
\section{A section}
Some text.
\end{document}

articleor something based upon it, but that's everything my crystal ball is able to tell me for now... – campa Apr 12 '21 at 13:46memoirclass\partis on a page by itself. – Peter Wilson Apr 12 '21 at 17:32