Doxy_db composes sqlite3 databases generated by Doxygen into multi-section manuals that have a simple query API.
doxy_db leverages improvements to Doxygen's sqlite3 generator which were first available in Doxygen 1.8.15 (though there have been a few rounds of regressions and fixes since then). For the best experience, I recommend starting with Doxygen 1.9.7+.