I would choose Rust. Today it might be that the market has more jobs on C++ and there are more codebases.
In the future, those codebases will only be the legacy ones and you will end up doing more maintenance with C++.
With Rust your investment of today will pay off in a few years.
Deciding what to learn today is an investment decision and you should look into what you think the future will look like. To me it looks Rusty. :-)