GTK apps can support the global menu. There's a GTK plugin that adds support, and many distros install it by default. I think it was originally written by Canonical (their custom Unity desktop also used a global menu bar).

Not sure about the state of things with Electron. I'm sure you're generally right and there are some gaps, and of course, on Mac OS you do only very rarely encounter an app with an empty menu bar (I have though).