It’s possible that most of old X11 toys would not work properly, because many of them rely on X11 drawing APIs, but they are pretty simple to implement anyway.

I gave it a quick go and very few things work at the moment. None of the programs you listed do.

From the README:

  At the moment it can render simple applications that do GLX, EGL or Vulkan graphics (fully hardware accelerated) nested in an existing X server.

And that sounds about right. As far as I can tell it doesn't yet have a lot of the core X11 stuff that "normal" clients expect. For example xterm doesn't start because requests like X_AllocColor, X_OpenFont, X_PutImage (a few picked at random from the error output) are not implemented yet.

glxgears on the other hand does work :)

motif apps? xmag? xfontsel? forwarding over ssh? ~/.XCompose? "links2 -g"?