Think it’s hard to find exact details for their generation procedure. From online comments in various places my guess would be:
MSDN: Sandcastle type doc engine
Xamarin: MonoDoc revision by the looks of it
MSDN seems to have locked down their doc generation tool - sandcastle since 2012. Since then a opensource project has the equivalent for Managed projects. Not much luck for native languages. Xamarin - did not look too hard tbh. Think their’s is the least of the three I prefer.
QDoc seems a nice tool from basic skimming through:
QDoc Commands seem quite extensive and seem to cover every requirement within Qt documentation itself. Also has the benefit of being cross-OS and already bundled with the super project for integration.
Might be a nice task to try and check the output on a new project.