This highly depends on what it is you’re trying to build. If it’s a simple CRUD backend + database, then there’s really no reason to use Rust except if you just want to. If it’s doing heavy computation, then you’d want to benchmark both and see if any potential gains by writing it in Rust are worth the effort of using Rust over Node.js.
Practically speaking, it’s really uncommon to need to write a backend in Rust over something like JS or Python. Usually that’s only needed for high throughput services (like Cloudflare’s proxy service which handles trillions of daily requests), or ones performing computationally expensive work they can’t offload to another service (after benchmarking first of course).