Maybe. Gtk and its related libraries don’t cover everything Qt does, but they’re not small either. It’s also fair to include the native toolkits themselves on their respective platforms that are written in a mixture of C++/C/Objective C.
I also will point out that one of the cross platform toolkits with some traction in the Rust world is amusingly fltk.
> What grandparent probably means something that leverages parallelism and/or GPU acceleration.
You mean like QtQuick/QML, skia (basically this is the effective underpinning of electron and flutter) or Dear Imgui, etc. There are a handful of widely used GPU based GUI libraries. The above examples are all C++.
> leverages parallelism
The memory model of Rust is still whatever C++ does. I get that Rust has some nice features and C++ makes it easy to fuck your self but people have been doing large scale parallel software development for years in C++.
> Qt is also old as Jesus, and making a cross OS GUI is extremely hard.
The claim was we are in a new era of “leverage” that will make the hard very easy (that’s what it sounded like at least). I found the claim at best vague and low on specifics or evidence - hence the mention of RESF.