I've been hunting errors in the docs build logs, and I found that the cpp-concept example (located in examples/specific) was not being properly parsed by doxygen in the CI. It is parsed as expected in doxygen v1.9.2 (&1.9.3) per local testing.

My error hunting goal is to make sphinx treat a warning as an error, thus making the doc building CI runs fail when new warnings have not been addressed. Due to this issue, we'd have to pin CI runs to doxygen v1.9.2 or newer (which can be done per #782 ). There is also a way to use conda forge to make RTD builds use a specific version of doxygen (despite the runner's frozen PPAs) which is a simple change in readthedocs.yaml.