dist/s_docs selects a Doxyfile based on an exact-match case statement against the installed doxygen version string:

1.8.17 → Doxyfile
1.9.1 → Doxyfile.9
1.9.3 → Doxyfile.9
1.11.* → Doxyfile.11

This has two problems. First, any version not in the list — including 1.8.16, 1.9.2, 1.9.4, 1.9.5, or anything in the 1.10.x range — silently exits 0 and skips doc generation with no indication of what to do.

Also, Doxygen 1.11.* is ancient. A Homebrew install of Doxygen today gives you 1.17.

Update s_docs to be future-proof.