Yes, clearly the new releases of 3.22 and/or 3.24 just suffer from the same
problem (3.22 does not work, and stable is either that or 3.24),
and it's going to keep happening and become more of a problem until someone fixes it. Either way, there is a bug for it (see below), and unfortunately all of us just posting "me too" doesn't help fix that.
This seems to require someone from the GNOME documentation site helping out the gtkmm team, because they haven't conclusively figured out the problem or a fix, otherwise the bug would be resolved:
https://gitlab.gnome.org/GNOME/glibmm/issues/26
In terms of a quick workaround The latest gtkmm docs that work are 3.20; substitute "3.20" for "stable" in any doc URLs, and hope the old docs are still accurate enough, or just read the header Doxygen documentation. For glibmm, the substitution for stable will be 2.52 I would guess (at least that's what I most recently used).
