Shouldn’t this be easily available in Electron/Tauri and React Native apps?

Electron doesn't use WebKit, so definitely not. Not sure about Tauri desktop, but how would you use it for Tauri mobile and React Native?

Woah, TIL. Chromium apparently forked WebKit in 2013. wtf?

So, if you wanted webviews that could leverage this you’d basically need a native swift app with webviews to get access.

Even if you could get it you wouldn't be able to publish it on the App Store due to the permission it requires.

React Native / Expo apps can get liquid glass via the actual underlying native ui elements.