I've noticed the camera AR from Vuforia show always a black screen when ARM64 is set in Build Settings into Unity. Evrything works fine when ARMv7 is checked.
There is clearly a bug with ARM64 IL2CPP compiling mode with Vuforia / Unity. I'm using Vuforia 8.0.10 with Unity 2018.3.3 on Windows 10. I have download the last samples from the asset store (which bring also black screen when ARM64 is checked).
I have made the test with 3 different phones, Sony XPERA XA2, Samsung A5 2017 and Huawei with Android 8.0. The problem is exactly the same on the 3 phones. A clue is there is not request authorization at the app launch for the camera use when ARM64 is checked but there is the request when ARMv7 is checked. It seems there is a problem whith request authorizations when ARM64 is selected.
In August 2019, we won't have the choice, ARM64 will be our only choice to publish Android app on the Google Play Store. ARMv7 and Mono apps will be rejected by Google. Can you please see what is the problem ?
By the way, I have made a test with the following trick:
Replacing Microphone in the example with Camera, Android is correctly asking me my authorization to use the camera but the screen stays black once the AR scene is loaded. The only thing wich works is to change ARM64 to ARMv7.