that's bullshit. I use Qt apps and they are still in 2022 able to use X11 paint commands to render over the network in a way that is much, much, much more fluid than e.g. rdp, vnc or whatever other bullshit like that. Many GTK apps also seem to work fine (though not all, Geany is snappy while Gimp isn't for instance)
see how it looks: https://streamable.com/t9foij