How do modern languages deal with prototyping and modules internally?

In my journey to learning C, I've come across header files, which are used to (I'm assuming) define a prototype for the source file, as well as structure modules. This feature, in my opinion, is pointlessly not just redundant, but possibly a source for pitfall. The same information can probably be extracted from the source code, if not for the restrictions of the language specification in C.

Say, if I have a GTK project, I will have to use the preprocessor directive, that will require the use of GTK headers that look something like #include <gtk/gtk.h>, and they're usually in the system path. How do modern languages, like Rust, Zig or Go deal with this situation, where shared libraries are used?