[jll29]

I assume you know an older form of C++; the language changed a lot over the years, and the more recent features are "better" but they also make C++ (even) more complex. It suffers from ugliness, non-orthogonality, over-complexity, among other diseases, but it is still somewhat practically relevant. Rust is worth learning for its 1. avoidance of null and memory leaks 2. great error handling 3. excellent compiler error messages 4. concise notation (perhaps except macros, Common LISP wins here IMHO).

So first learn Rust, later learn C++11+ (by the time there will be a successor of C++11 that may look even less like the C++ you know).

Learning Rust will develop your thinking and taste, and this will then help you judge the flavour of C++ that you will be learning later (and because you'd update your C++ skills later, you may skip another C++ legacy flavour in the process).