I can't answer your question, nor am I in a position to pitch Tauri however it has been suggested and it sounds like you investigated it. However, I can suggest an alternative if you are super unhappy with the stack and can't rely on the frameworks that is controversial - Rust core plus Electron for GUI.
1Password does this. It's not sexy but it works, and if you're building a product you need something that is mature and works. It's probably an easier port from Sciter than Flutter.
You didn't really ask, but this combination is likely a reliable path forward. If you keep web technology maybe Tauri would mature to the point you are happy with it and could switch one day. Not really easy to suggest someone rewrite parts of their product but if the tech is not doing it for you then it's nice to at least have a card to play.
Having something purely in Rust would be nice but GUI wise it just isn't widely used enough. egui and iced are mentioned a lot - the latter is at least adopted by PopOS, but that's not enough for me to bet on yet.
