You're being needlessly dismissive.

From a philosophical perspective, there's no way to know that any piece of software is truly correct without formal verification.

But in the present, non-philosophical context, it's obvious that what we mean is, colloquially, "how well-tested is this against a variety of edge-case files which the official winrar handles correctly? Is there a test suite, and how robust is it? Plenty of software that claims to be compatible with the rar format, doesn't actually successfully read all rar files."

It's also equally obvious, in the present context, that we would prefer these steps to have been taken by the author of the software before we install it and run it on our own computers and data. The parent commenter wasn't just asking about the software's correctness for the sake of academic curiosity.

I hope the developers of, say, the brakes in my car don't interpret 'software correctness' the way you do.

Added, later: hey you changed your comment, added a whole paragraph.

    use std::fs::File;
    use std::io::prelude::*;
    
    fn main() -> std::io::Result<()> {
        let mut file = File::create("content.txt")?;
        file.write_all(b"3!")?;
        Ok(())
    }

> This is Rust we're talking about. It doesn't even need to work; as long as it compiles, it's correct.

No, it doesn't even need to compile. The mere fact that it's in Rust means it's correct.