Is there a way to declare in the preamble so that the tablenotes environment has:
- Single spacing between the item-lists.
- The size is
\scriptsize.
\documentclass[a4paper, 12pt]{article}
\usepackage[sfdefault]{atkinson}
\usepackage{threeparttable}
\begin{document}
\begin{threeparttable}
\caption{Test table}
\begin{tabular}{c c c}
Test & Test & Test\tnote{a}\\
Test & Test & Test\tnote{b}\\
\end{tabular}
\begin{tablenotes}
\item [a] Note 1.\\
\item [b] Note 2.
\end{tablenotes}
\end{threeparttable}
\end{document}

\appto\TPTnoteSettings{\scriptsize}-- doesn't seem to work if thethreeparttablepackage is loaded with the optionflushleft. Replacing\appto\TPTnoteSettings{\scriptsize}with\AtBeginEnvironment{tablenotes}{\scriptsize}, though, would appear to be robust to using the package'sflushleftoption. – Mico Oct 19 '21 at 20:55