Bevy is written in Rust and according to https://github.com/rive-app/rive-bevy/, the backend used for the integration uses Vello (also Rust), not the Rive renderer. Could be that integrating Vello into the C++-based Godot would be finicky. With the Rive renderer open-sourced, maybe both Rive and Godot will see an integration using the Rive renderer?

Never tried using it, but this github repo shows rive + godot4 in some fashion

https://github.com/kibble-cabal/godot-rive