> Electron is problematic and you can always tell an Electron app when you see it because the performance is so terrible.
Have you tried the open-source Brave browser?
Its GUI is created with Muon (which is a fork of Electron). The browser doesn't seem very slow, at least to me.
Also, Firefox have used XUL for a long time to create its interface. XUL is not much different from what Electron is: XML-like markup to design your interface and JS to manipulate it.