It appears to be related to the bug peterlaw mentioned here https://www.kokosoft.pl/forums/topic/cannot-trigger-the-inappbrowser/
When you build without “Portrait” and “Portrait Upside Down” options inside of Unity onto a Device on iOS 13+ innAppBrowser will behave strangely like I mentioned above.
If you build it onto iOS 12 or before, it works fine with the other options disabled.
My app needs to be able to rotate, and have both portrait and portrait upside down disabled. Do you know of a way I could get around this? Or will this need an update?