The more languages you learn, especially with reusable concepts, the less of a tax it is to learn a new one. As someone who has written C/C++ for over a decade, learning Rust felt very straightforward -- I just had to learn about the borrow checker, and it was fairly straightforward to reason about how it works based on my knowledge of unique pointers in C++.
I certainly don't think C++ is a prerequisite to learning Rust, but I do think your path to deeply understanding Rust will accelerate if you understand C (or specifically, understand pointers and heap allocations). But to each their own!
Learning new languages is certainly useful/important, but time is finite. The idea of learning a certain language as a bridge to another is unrealistic unless one has a _lot_ of time.
I certainly don't think C++ is a prerequisite to learning Rust, but I do think your path to deeply understanding Rust will accelerate if you understand C (or specifically, understand pointers and heap allocations). But to each their own!