The firstaid fix for pgfmorepages is not correct.

[loopspace]

In latex2e-first-aid-for-external-files.ltx there is a fix for how the pgfmorepages package hooks into the shipout routine. This is a direct copy of the fix for the pgfpages package, but the two packages hook into the shipout routine slightly differently: pgfpages applies its hook at the end of the package but pgfmorepages applies its hook via an AtBeginDocument call.

To that end, the fix for pgfmorepages should patch the pgfmorepages hook rather than try to override its effect. The following is what I think it ought to be:

\AddToHook{file/after/pgfmorepages.sty}[firstaid]{%
  \cs_set_nopar:Npn \pgfhookintoshipout {
    \cs_set_eq:NN \pgfpages@originalshipout \tex_shipout:D
    \cs_set_eq:NN \tex_shipout:D \pgfpages@interceptshipout
  }
}

Some MWEs.

Currently not working:

\documentclass{article}

\usepackage{pgfmorepages}
\usepackage{lipsum}

\begin{document}

\lipsum[1-4]{}

\end{document}

Currently working:

\documentclass{article}

\ExplSyntaxOn
\makeatletter
\RemoveFromHook{file/after/pgfmorepages.sty}[firstaid]
\AddToHook{file/after/pgfmorepages.sty}[firstaid]{%
  \cs_set_nopar:Npn \pgfhookintoshipout {
    \cs_set_eq:NN \pgfpages@originalshipout \tex_shipout:D
    \cs_set_eq:NN \tex_shipout:D \pgfpages@interceptshipout
  }
}
\makeatother
\ExplSyntaxOff

\usepackage{pgfmorepages}
\usepackage{lipsum}

\begin{document}

\lipsum[1-4]{}

\end{document}

[FrankMittelbach]

now on ctan

[loopspace]

Thank you!