There is no safe way to detect the highest available OpenGL version with shared contexts

Hello,
I need to set the highest available GL version that I can detect on my users's computers (as they may submit their own shaders directly - which potentially use more recent features that I can expect, especially on app startup).

So, to detect what I can use, I would like to run more-or-less the following upon app startup, to try and make a context with the highest available version in descending order and stopping when I have something that works:

    std::vector<std::pair<int, int>> versions_to_test = {
        { 4, 7 }, { 4, 6 }, { 4, 5 }, { 4, 4 }, { 4, 3 }, { 4, 2 }, { 4, 1 }, { 4, 0 },
        { 3, 3 }, { 3, 2 }, { 3, 1 }, { 3, 0 },
        { 2, 1 }, { 2, 0 }
    };

    QOffscreenSurface surf;
    surf.create();
    QSurfaceFormat fmt = QSurfaceFormat::defaultFormat();
    for(auto [maj, min] : versions_to_test) {
      fmt.setMajorVersion(maj);
      fmt.setMinorVersion(min);

      QOpenGLContext ctx;
      ctx.setFormat(fmt);
      if(ctx.create())
      {
        if(ctx.makeCurrent(&surf))
        {
          break;
        }
      }
    }
    fmt.setDefaultFormat(fmt);

The problem that I encounter is:

• If I run this code before QApplication instantiation, then I get a crash because it's likely too early to create QOffscreenSurface.. makes sense.
• If I run this code after QApplication instantiation, with AA_ShareOpenGLContexts, then the shared context has already been created during QApp construction, thus it's too late.

In that case, what can I do (except resorting to platform-specific code...) ?