You could try OCaml (it does have exception but they're usually "opt in"), it's a really nice language and probably one of the closest to GC'd Rust. There's also Swift that inspired some features.
Flowtype has horrible performance, which in my opinion partially explains why it has lost so many users to Typescript, which has much more predicable and fast performance even though it's written in JS. The project is basically dead
About Flow, I've never used it so I can't say, but Rescript (which is written in OCaml) compiles 10 to 100 times faster than Typescript.
Darklang is being rewritten to .Net because they were unsatisfied with the OCaml ecosystem.
Horrible performance is generally more a question of algorithms and software architecture than a problem with a language, which only account for a flat percentage of performance.