It's not just the WebKit bit, basically the entire app implementation is actually shipped as a "Private Framework" which lives outside the .app bundle. e.g. on macOS % otool -L /Applications/Safari.app/Contents/MacOS/Safari /Applications/Safari.app/Contents/MacOS/Safari: /System/Library/PrivateFrameworks/Safari.framework/Versions/A/Safari (compatibility version 528.0.0, current version 623.1.14) /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1356.0.0)

There's a bunch of other private frameworks (SafariCore.framework, SafariFoundation.framework, SafariPlatformSupport.framework, SafariShared.framework, SafariSharedUI.framework, SafariSwift.framework) as well. I haven't checked but I assume it's similar on iOS.

Not in the EU...

While alternative browsers are legally usable on iOS, nobody has really published one yet.

Maintaining a browser is expensive and with the way Apple implemented their obligations, it's not worth it for existing browser companies to ship their own engines (and have twice or more the maintenance).

Yes in the EU. Apple made the alternative browser requirements impossible to meet, and somehow got away with it.

Yes also in the EU.