evaluateJavaScript callback is significantly slow on macOS 26.2 for iOS App on Mac

Hello,

After upgrading to macOS 26.2, I’ve noticed a significant performance regression when calling evaluateJavaScript in an iOS App running on Mac (WKWebView, Swift project).

Observed behavior

• On macOS 26.2, the callback of evaluateJavaScript takes around 3 seconds to return.
• This happens not only for:

evaluateJavaScript("navigator.userAgent")

but also for simple or even empty scripts, for example:

evaluateJavaScript("")

On previous macOS versions, the same calls typically returned in ~200 ms.

Additional testing

• I created a new, empty Objective-C project with a WKWebView and tested the same evaluateJavaScript calls.
• In the Objective-C project, the callback still returns in ~200 ms, even on macOS 26.2.

Question

Is this a known issue or regression related to:

• iOS Apps on Mac,
• Swift + WKWebView, or
• behavioral changes in evaluateJavaScript on macOS 26.2?

Any information about known issues, internal changes, or recommended workarounds would be greatly appreciated.

Thank you.

Test Code Swift

class ViewController: UIViewController {
    
    private var tmpWebView: WKWebView?

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        setupUserAgent()
    }
    
    func setupUserAgent() {
        let t1 = CACurrentMediaTime()
        tmpWebView = WKWebView(frame: .zero)
        tmpWebView?.isInspectable = true
        tmpWebView?.evaluateJavaScript("navigator.userAgent") { [weak self] result, error in
            let t2 = CACurrentMediaTime()
            print("[getUserAgent] \(t2 - t1)s")
            self?.tmpWebView = nil
        }
    }

}

Test Code Objective-C

- (void)scene:(UIScene *)scene willConnectToSession:(UISceneSession *)session options:(UISceneConnectionOptions *)connectionOptions {
    
    NSTimeInterval startTime = [[NSDate date] timeIntervalSince1970];
    WKWebView *webView = [[WKWebView alloc] init];
    dispatch_async(dispatch_get_main_queue(), ^{
        [webView evaluateJavaScript:@"navigator.userAgent" completionHandler:^(id result, NSError *error) {
            NSTimeInterval endTime = [[NSDate date] timeIntervalSince1970];
            NSLog(@"[getUserAgent]: %.2f s", (endTime - startTime));
        }];
    });
}