We can provide a groff option for --pdf-engine, using groff -Kutf8 -et -ms -Tpdf.

When groff is being used, we need to avoid escaping the strings in .pdfref O macros (see the linked discussion). This could be done in two ways:

a. Add a groff extension to ms (-t ms+groff) that triggers the non-encoded behavior. Or:
b. Just "unescape" the encoded strings in Text.Pandoc.PDF before passing to groff.

Option a would allow you to produce a .ms file that you process manually with groff, so it's probably better. The groff extension could be added automatically when groff is selected as pdf-engine.

MAYBE: change default font family in the template to T, since this works better on macOS with the broken homebrew groff install (see linked discussion).

Discussed in #10720