Although I must admit, I'm disappointed that they didn't use react-native-web to build this app in a cross-platform way. I agree Electron is a good choice for the current landscape, but I'm hopeful that we will be able to move past it. If Sonar was implemented with React Native's layout API, it would be easily portable to projects like react-native-macos, React Native on Windows, or projects like Proton Native, once it matures and stabilizes.
Of course Emil knows this, because he is one of the primary maintainers of Yoga, the cross-platform flexbox implementation in React Native. This is one of the primary technologies that will allow us to move away from Electron one day, if people would just stop using CSS!