Earlier quoted context omitted.
Even Rust has an unsafe subset. There's a meaningful question about how to make such an unsafe language as easy and comfortable to use as possible, and Zig is a decent answer to that particular question. The libraries Zig ships with are especially relevant here, rather than the core language per se: Rust's library facilities are outright terrible to write unsafe code with, because the usual requirements of safe code…
"Like unsafe Rust, but more convenient to use" is basically every imperative language around there, I still don't understand the specific niche that Zig intended to fill
It's weird to talk about "basically every" language, when you have exactly three mature systems languages: C, C++, Rust. C is from the 70s, C++ is an incoherent kludge on top of it, and Rust has a miserable DX (especially when actually used as a systems language instead of relying on pulling in 500 cargo dependencies that handle the unsafe code for you). Nothing else is used for serious systems programming. You don't need to do anything innovative, simply developing C-but-with-some-lessons-learned-since-1972 to a mature enough point would be more than sufficient to add value to the pitiful array of language options available. It is the language projects that try too hard to be novel and innovative and do brand new things that don't fill a real niche; they are academic experiments that will be use at most recreationally, never for real projects. If Zig doesn't seem interesting or unique enough to you, that's a good sign for it, because a new systems language doesn't need to be interesting or revolutionary.