mwe.tex

\documentclass[11pt]{report}
\usepackage[withpage, printonlyused]{acronym}
\usepackage{subcaption}

\begin{document}

    \ac{FYI}.

    \begin{figure}
        \caption{\ac{TLA}}
    \end{figure}

    \begin{acronym}[TLA]
        \acro{FYI}{for your information}
        \acro{TLA}{three-letter acronym}
    \end{acronym}

\end{document}