There have been various in https://bugzilla.gnome.org/show_bug.cgi?id=141154, first one in 2011 I believe. There are a few more not mentioned there, such as https://github.com/Dudemanguy/gtk and https://gist.github.com/ahodesuka/01213036b58e510dc074

I personally don't care as one can use flatpak portals nowadays (qt makes it really easy for non-flatpak applications to use, but I haven't seen how I can do it in non-flatpak gtk applications).