(I'm going to write about Rust learning resources in general, so this may not fit the question, but believe the concepts are still worth considering)
Rust is a very hard language to learn, not only because of the inherent difficulty, but also because of the lack of a structured way to approach the learning itself.
Reading codebases is a very good practice in programming, but I don't think it benefits below the intermediate (if we put it this way) level, as you may not even notice many of the design choices.
You're going to need a lot of time to become fluent, so it's crucial to clarify what's your target. If you just want to play with the language, anything will do; if you're serious, it's important to follow a path that it's stimulating, otherwise, you will just get bored and stop.
I've tried Rustlings as a beginner, but it wasn't very stimulating. Gjengset's videos are extremely slow - they could be cut to a third, and still keep the same content; again, not very stimulating.
For beginners, a possible path is to study the reference book (there's no escape from that), then optionally find a "strongly guided" projects-based book, then find some projects to work on (which may include "weakly guided" project-based books).
A project-based book I suggest is "Rust Programming By Example" (Packt). The code quality is not very good, but it has several different projects to play with.
Another book that may be interesting is (I haven't read it yet) is "Hands-on Rust- Effective Learning Through 2D Game development" (Pragmatic Bookshelf).
After you're past the strongly guided projects phase, you may start to work on weakly guided ones. Two very good books (by the same author) are "Mazes for Programmers" (Pragmatic Bookshelf) and "The Ray Tracer Challenge" (Pragmatic Bookshelf).
After that, sky's the limit, as you'll be surely ready to join established projects. The "Rust weekly" newsletter publishes projects who welcome beginners.
You may want to read, at some point, "Programming Rust" (O'Reilly). It's tedious to read it after the reference book, but it has a different, slightly more in depth, view on the Rust language.