Using OpenGL is possible, but the Metal framework still needs to be added to the project, otherwise our library won't link properly and that's why you're getting the error message.
Regarding the original issue, is the problem that starting the camera is too slow? Could you reproduce it with our sample project as well, or just with your project?
I've got weird results with iOS app. It loads about 10-15 seconds after the splash screen to the Wikitude camera view, when Android app does it in ms. I've tested it on iPhone 7 Plus and 8 (both iOS 13) and with Android on Huawei Mate 10 Pro and Samsung Note 10+. I'm using the newest Unity 2019.2.10f and Wikitude 8.9 (2019_09_24_03_43_11), Xcode 10.1 and 11.1 tested. Player Settings for Android and iOS are the same/default.
I've read this could be a problem with Graphics API, but I can't use OpenGLES2 or 3. It only works with Metal, otherwise it fails during build for arm64 with error like this:
Have you faced such as problems?
Thanks in advance.