I use the latest version (2.0.2) of the InAppBrowser plugin
Unity 2019.2.15
MacOS Catalina
Xcode 11.3.1
The Plugins/iOS dir has:
InAppBrowserViewController.h
InAppBrowserViewController.mm
InAppWebBrowser.a
iOSInAppBrowser.mm
ISN_NativeCore.h
ISN_NativeCore.mm
OrientationNavigationViewController.h
OrientationNavigationViewController.m