Correctly initializing GDK when using Qt

Hello,
consider the following code:

#include <QApplication>
#include <QLabel>
#include <dlfcn.h>

int main(int argc, char** argv)
{
  using gdk_init_check_ptr = void *(*)(int*, char***);
  auto gdk = dlopen("libgdk-x11-2.0.so.0", RTLD_LAZY | RTLD_LOCAL);
  auto gdk_init_check = (gdk_init_check_ptr)dlsym(gdk, "gdk_init_check");

  gdk_init_check(nullptr, nullptr);

  QApplication app{argc, argv};

  QLabel label{"foo"};
  label.show();

  return app.exec();
}

It will work fine if the QT_QPA_PLATFORMTHEME is not gtk3.
Otherwise, it either hangs (if gdk_init_check comes before QApplication) or crashes (if gdk_init_check comes after), likely because QGtk3 calls it too (through gtk_init).
Sadly qgtk3 is the default platform theme on Ubuntu means that's where are a lot of users.

What are my options to make sure that things work correctly no matter my user's platform themes ? My app loads external plug-ins from separate vendors and some require a GTK context to be initialized.