https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101258
--- Comment #18 from Jonathan Wakely <redi at gcc dot gnu.org> --- The main problem with trying to rely on doxygen is that it's very buggy and simply refuses to generate good docs for some entities, even though they are correctly documented. See the commit message above, and see https://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-api.20210701.html/a01556.html where it refuses to put filesystem::path in the relevant module despite @ingroup being used. And https://github.com/doxygen/doxygen/issues/8633 causes some entities to be undocumented, because doxygen can't parse whitespace between tokens. Obviously nobody is going to create something better than doxygen just for libstdc++, so it's the best option we have.
