\end{filecontents*}
\documentclass[letterpaper]{article}
\usepackage{fontspec}
+\usepackage[default]{fontsetup}
\usepackage[greek.ancient,english]{babel}
\babeltags{grc = greek}
\babelfont{rm}{Old Standard}
\babelfont[greek]{rm}[RawFeature={+ss05;+ss06}]{Old Standard}
-\babelfont{sf}{NewComputerModern Sans}
-\babelfont{tt}{NewComputerModern Mono}
\newlength\defaultparindent
\setlength\defaultparindent{\parindent}