initialUserScripts property
Initial list of user scripts to be loaded at start or end of a page loading. To add or remove user scripts, you have to use the InAppWebViewController's methods such as InAppWebViewController.addUserScript, InAppWebViewController.removeUserScript, InAppWebViewController.removeAllUserScripts, etc.
NOTE for iOS: this property will be ignored if the WebView.windowId has been set. There isn't any way to add/remove user scripts specific to iOS window WebViews. This is a limitation of the native iOS WebKit APIs.
Implementation
final UnmodifiableListView<UserScript>? initialUserScripts;