First, what do you mean by “C is just so old”? That seems like a language problem, not a GTK problem. Tbh, when it comes to documentation, you’re likely better off with C as the official GTK docs targets the C API (https://docs.gtk.org/gtk4/).
Also, what do you mean by “it doesn’t translate well to Rust”? Because, Rust, like other supported langs like Python, have bindings that are equally well-documented to an extent. I haven’t used the Rust binding but I’ve used the Python binding extensively and there are references to all the APIs (https://lazka.github.io/pgi-docs/)—same with Rust (https://gtk-rs.org/gtk4-rs/).
Lastly, I can understand not using GTK for cross-platform apps, but not for the reasons you mentioned. While GTK’s primary target is Linux, you can technically still make it cross-platform.
Your statement about C is still mostly wrong. First, linting isn’t typically a built-in feature for many languages; you mostly depend on external tools or IDEs (for C/C++, CLion and VSCode with specific extensions solve this). A similar occurrence is seen in formatting, where, except for a few languages like Rust and Go (with officially maintained formatters), you still have to depend on external tools or IDEs. For dependency management, it is well-known that C/C++ lacks an official package manager, but there are well-tested third-party package managers such as conan (https://conan.io/) and vcpkg (https://vcpkg.io/). Another benefit is the project-local support in both package managers (although it is more robust in Conan), which effectively addresses both the version management and virtual environment issues you raised. You don’t always need virtual environments anyway (Rust doesn’t use one either).
I haven’t used the Rust binding, so I don’t have direct experience with this and may not fully understand the pain points. However, a glance at the docs shows the Rust binding and trait-based pattern still does the job effectively. I don’t understand what you mean by “weird structures split into multiple modules”, as you’re just reusing built-in structs like you would use a class in the Python binding, for instance. So I don’t see the problem.
Well, mobile support for GTK is currently experimental, so there’s that.