Problem persists in Xcode 26 Beta 5.

I have opened FB19354105 with a small sample project to reproduce the problem. It turns out the code in AppDelegate is not relevant for the problem, it occurs if the storyboard includes a UIToolbar.

Having the same problem with my app: getting error *** Terminating app due to uncaught exception 'NSInvalidUnarchiveOperationException', reason: 'Could not instantiate class named TtGC5UIKit17UICoreHostingViewVCS_21ToolbarVisualProvider8RootView because no class named TtGC5UIKit17UICoreHostingViewVCS_21ToolbarVisualProvider8RootView was found; the class needs to be defined in source code or linked in from a library (ensure the class is part of the correct target)' when using Xcode 26 beta 4 and running on iOS version < 26. I have opened FB19354105 with a small sample project to reproduce the issue.

Same problem after update to iOS 18.6.

Found it (via https://trac.webkit.org/changeset/261940/webkit) - to force the old iPad behavior set _webView.configuration.defaultWebpagePreferences.preferredContentMode = WKContentModeMobile;

If the WKWebView has already been initialized via Storyboard, you can simply set _webView.configuration.defaultWebpagePreferences.preferredContentMode = WKContentModeMobile;

Thank you for your reply, I appreciate it. (Also, by the way: thank you for the feature of model encryption - it was much needed.) While available for more than 2 years, I only now switched to an encrypted model and currently in the process of testing it - so this is quite a coincidence. Based on your reply, I will stick with my current error message.