I think if you're going to use Rust on front end you're probably going to use it on back end too. In that case, I would just use Dioxus and get the e2e typing for free. What would be the benefit of Sycamore?

I wouldn't recommend e2e Rust generally yet though. I think server/API + web could work, but mobile is just boiling the ocean and will never be as good as native. You might think you can just use it for server/API + web, then do native mobile apps, but actually the escape hatches in all the frameworks I've used are not great.

Sad to say but "just use React" remains the good advice.