I think what you mean when you say instance of Gtk is a copy of the Gtk library in memory? That's not how flatpak works; identical libraries will share the sam

I think what you mean when you say instance of Gtk is a copy of the Gtk library in memory? That's not how flatpak works; identical libraries will share the same file on disk and will only be loaded once, just like non-flatpak apps. And because Gtk is usually part of the runtime most apps will use one of a few versions.