Most of what gives high-reliability or high-assurance code that label is the process rather than the language. In colloquial terms it rigorously disallows sloppy code, which devs will happily write in any language given the chance.
As much as C is probably the least safe systems language, and probably my last choice these days if I had to choose one, more high-assurance code has probably been written in C than any other language. Ada SPARK may have more but it would be a close contest. This is because the high-assurance label is an artifact of process rather than the language.
Another interesting distinction is that many formalisms only care about what I would call eventual correctness. That is, the code is guaranteed to produce the correct result eventually but producing that result may not be produced for an unbounded period of time. Many real systems are considered “not correct” if the result cannot be reliably delivered within some bounded period of time. This is a bit different than the classic “realtime systems” concept but captures a similar idea. This is what makes GCs such a challenge for high-reliability systems. It is difficult to model their behavior in the context of the larger system for which you need to build something resembling a rigorous model.
That said, some high-assurance systems are written in GC languages if latency is not a meaningful correctness criterion for that system.
If I was writing a high-reliability system today, I’d probably pick C++20, Zig, and Rust in that order albeit somewhat in the abstract. Depending on what you are actually building the relative strengths of the languages will vary quite a bit. I will add that my knowledge of Zig is more limited than the other two but I do track it relatively closely.