Contribute an advanced feature to an existing project or start a project from scratch
Start a project for yourself, your dog, your organization or mother. This might be a microservice, library or small tool. Everything is possible.
Another option is to contribute to an open source project that you like or may want to strongly depend upon in the future.
See section (5) about your first contribution for some inspiration on where to start.
As it is assumed that at this point you are doing intermediate level work in Rust it will be the case that sooner or later you'll need to debug. Or perhaps you are about to deploy your own small project to production. In any case, you'll need to know how to debug Rust applications. You can read all about this and tracing in Appendix VIII. Debugging Rust.