OP is describing they want to write a backend, not a operating system. "Systems language" might have been a "kinda" specifier, rather than precise.

Go, Kotlin, C# or even Java works just fine for backends. If I were OP, I'd use whatever I know best, or is the most similar to what I know best. Unless I want it to be a learning experience, they I'd chose the language that is the least similar to the languages I know.

And then OP lists only C++ and Rust. Both known well for having no garbage collector. I think my comment is still valid.