os_setenv .. " TEXINPUTS=." .. localtexmf()
      .. (checksearch and os_pathsep or "")

\documentclass{article}

\ExplSyntaxOn

\cs_set_eq:NN \oldfigure \figure
\cs_set_eq:NN \endoldfigure \endfigure
\tl_new:N \l_env_body_text
\RenewDocumentEnvironment{figure}{ O{htbp} +b }{
  \tl_set:Nn \l_env_body_text { #2 }
  \begin{oldfigure}[#1]
    \tl_use:N \l_env_body_text
  \end{oldfigure}
}

\ExplSyntaxOff

\begin{document}

\begin{figure}[htb]
  This is a figure.
  \caption[ab c]{A BC}
\end{figure}

\end{document}

\documentclass{article}

\usepackage{endnotes}

\begin{document}

\theendnotes

\section{Section 1}

\endnote{1}\par
\endnote{2}\par
\endnote{3}

\end{document}