This is a simple, barebones template for a "Hello World" project that should help with getting started in Godot 4 with Rust.
This was made using Godot 4 Beta 14, and a pre-release version of GDextension. With this being said, since API changes may be made, slight revisions may need to be made if the repository is not kept up with but https://github.com/godot-rust/gdextension should have all info needed on what needs to be changed.
Enjoy :)