On the Vuforia Engine Release Notes page (https://library.vuforia.com/articles/Release_Notes/Vuforia-SDK-Release-Notes.html) in the Vuforia 8.6.10 section "Known Issues / Unity" it says that:
A black screen is seen when building a Vuforia for Unity as a Library app for iOS with XCode 11. Use Xcode 10.3 instead.
I believe there is a similar issue with version 8.6.7 as well. I created a version of the Unity-as-a-library project with Unity 2019.3.1f1 and Vuforia 8.6.7 following this article - https://library.vuforia.com/content/vuforia-library/en/articles/Solution/using-vuforia-engine-with-unity-as-a-library.html.
This Unity project appears to run correctly when built with Xcode 10.3, but causes an assertion when built with Xcode 11.3. The assertion (which occurs in vuforiaRenderEvent(int)) is:
validateRenderPassDescriptor:757: failed assertion `Texture at colorAttachment has usage (0x01) which doesn't specify MTLTextureUsageRenderTarget (0x04)'
I also find that this version crashes when Unity is unloaded (using the Unload button that appears in the sample) but this may be because I am not calling UnloadVuforia (Vuforia.VuforiaRuntime.Instance.UnloadVuforia() in C#) from the Swift/Objective-C side.
In my project I do not include any image or object databases or call any Vuforia functions. The scene just consists of a single Directional Light and an AR camera, with the usual Vuforia Behaviour script and the Default Initialization Error script.
I would like some advice about how to proceed. Will Xcode 11.3 be supported for this Unity-as-a-library purpose with the next release of Vuforia?
If it would help I could upload this project for reference.
(edit) I've been asked to tag @Cotora, Marius on this post.