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Yes. It makes JS run at ~30% speed, a worthwhile tradeoff given how often JIT bugs are used in exploit chains.

https://daringfireball.net/2024/06/apple_disables_webkits_ji...

This disables JIT for JSC (JavaScriptCore) system-wide. Third party apps never had been able to JIT on iOS, no permission to write executable pages.

Isn't it possible to used JIT for JSC in WebView?

WKWebView and SafariViewController do, but they run the browser engine and JIT in another process so that the app still doesn’t have the ability to execute unsigned pages.

Interesting! How are unsigned pages determined this case?

As far as I’m aware, JIT isn’t available to third-party apps on iOS and iPadOS.

System wide. This is documented